Oh boyo. Go out and get an oly set it will be the best decision you ever can make. Heres some advice I have given other people over time so if you have any questions let me know, if you can't already tell Im really into this stuff.
WOOT Finally something I can talk about! Now since you are wanting to get back into shape for a sport not just in general it would be a good idea to do some heavy conditioning, or whatever you can. For the core there are several things you can do two of the best that I personally do is the sledgehammer and tire workout, simply get a 10-20lbs sledgehammer and bang the shit out of a tree stump, tire, big pile of dirt or rocks.. just be careful. Now since the swinging motion with a hammer you might want to wait or be careful, you can always just do the chopping motion(like you were chopping down the tree) by starting around chest high with the hammer, slanted, then as fast as you can swing it down to hit your object. That right there is good conditioning and is a GREAT core workout.
For legs you could simply do squats with some sort of weight, i.e. a weighted bench, along with your hamstring curls and perhaps some sort of yoga. If you want to build muscle its a low amount of reps(usually about 3-6) of the highest weight you can properly perform at with that amount of weight. If you want stamina and conditioning its lower weight, higher reps. For these things you might want to invest time to make a sandbag, weight sled, suspension trainer etc as these things will give you the best workout when your wounded and will continue to do so afterwords.
DO NOT go with the B.S. Supplements, idk what your goals are but really since its been awhile since you've done any physical activity I would suggest getting some protein casein(helps with building up and muscle recovery, take at NIGHT) Also whey of protein would be good, take that 2-4 times daily depending how much you eat/work out. Creatine is a MUST for you, takes like two weeks to start seeing a result as your body requires time to get used to it but again helps with recovery.
DIET... doet. Stick with your complete protein foods(lean/red meats, fish) but if you eat incomplete proteins(plants, nuts, peanut butter) than compliment them with another incomplete protein such as bread or more nuts.
Remember to take a break 1-2 days a week and after 3 weeks take a week off, idk if you plan to do intense training or not, might be a good idea.
Food to eat:
Lean meats such as ham, chicken, pork chops etc for protein
steam veggies -if you STEAM them they maintain their nutrients
Fish -tuna, salmon and so on
Just eat anything with protein, carbs and low fat
Foods to avoid:
fast food
junk food
bad food
food with corn syrup
REMEMBER CARBS BEFORE WORKOUT, NOT AFTER!
Here are a list of exercises I suggest doing and are the ones I like to do the most myself.
COMPOUN

(works multiple major muscles @ once) *the idea of these is to build muscle, meaning use WEIGHT!*
Deadlift -Can be done with a sandbag or your standard barbell BEST THING EVER TO BUILD MUSCLE -works like 80% of your muscles, the squat takes care of the ones the deadlift doesn't
Squats - Can easily be done with a sandbag
Upper Bodydoy?)
Back Row- works upper back and shoulders
Chest Press -works your pecs, and gives the ladies something to look at -can be done with a weighted sled
Deltoid fly & variants - works the upper back, biceps and so on, there are several types of these you can do to work out different parts of your body -can be done with a weighted sled
Planks -classic
Core:
Planks -classic -one handed side planks work best, if not do it with your forearms on one side
Crunches -suspended, weighted, whatever.
Tire- get a big ass tire and flip it over up a hill
Sledgehammer -get a 10-20lbs sledgehammer, look for videos online on how to do it, and bang the shit out of something hard or a tire, stump etc
For the sledgehammer workout do
4 Minutes Banging the hell out of it, 2 minutes on left, 2 on right
1 Minutes rest
3 Repeats(of the 4 minutes and 1 minutes)
Total time est= 15 mins.
Lower Body:
Weighted Squats -get weight and squat
Hamstring Curls- fun, burns tho
Curls -best thing to do.
Forearms & hands: (grip strength)
One finger push ups -hard as hell, makes your fingers strong tho
Grippers - invest in one of these, cost like $20 for 100lbs of res and you basically squeeze it, improves your gripping str A LOT along with some forearm
Curls- get a dumbbell and curl it, good for forearms
As for working out there is A LOT you can do at home without actual weights trust me I train like that a lot and it will make you strong with functional strength. Other things you can use for training(some people might think your silly, but they WORK). You should stick to compound exercises that work multiple muscles, now just because you don't own actual weights doesn't mean you can't get fit if you want to. One way to workout at home is using nothing but your own body aka bodyweight training. The ONLY issue I see with this is eventually push-ups planks and squats won't be enough.. so I would suggest 'odd object lifting' for you.... DIRT CHEAP(even if you have to buy something its very cheap) and you can find a lot of it laying around or for free. So here are some ideas for you to look into, youtube and Google will help you out but I can start you with a list and simple explanations on what can be used.
*Power Sled... who said you have to buy one? You can make a simple sled out of two pieces of wood, or an old tire or anything that you can stack heavy objects in and drag. Its simple you can get some rope and tire and then put a few 50lb sandbags(3$ MAX per one at home depot) in it and drag it. With a sled you can also put rocks in it or anything heavy within reason. You can do exercises such as bicep curls, tricep extensions, you can just drag it to build total body strength. Just search on Google/YT for "Power(or weight) Sled workouts" and you'll get an idea. You'll also see it doesn't have to be a formal sled. People use a wide variety of things.
*Rocks... YES rocks. Rocks should be free, just go somewhere that has a lot of medium-heavier rocks(ones that you can lift but its somewhat difficult) and lift them. You can lift them then carry them, find smaller heavier ones and carry one in each hand to build GOOD grip strength(VERY important for martial arts) and other sort of lifts.
*50lb bags of sand. These can be found at home depot for about $3 tops and they can do wonders. You can do overhead presses with them, carry them, squat the sand bags if you stack a few of them and just lift them in general. Cheap and all you have to do is buy them then lift. Can also be used for your sled as CHEAP weight by just throwing them on your sled then dragging.
*Sledgehammers... You can buy one, find one or whatever and bang the shit out of stuff. Its pretty much that simple.
*Cars. Have a car or truck? If so then go to an EMPTY parking lot where no one will be and push/pull your car. I would suggest to look up videos of how to do this first on youtube but its pretty easy, its just so you don't bust your back or another part of your posterior chain. Great way to build good strength.
*Big logs. you can carry these, lift these, overhead press them and many other lifts. Should be free to find some decent size logs in decent weight to lift. Great things to use honestly.
*Kegs... get an empty keg and fill it with water, sand or cement and just carry it, drag it, press/pull it or do other things such as by lifting it up and resting it on the top of your delts and squatting it or doing good mornings.
*Your own body. Bodyweight exercises are good the classic dips(FANTASTIC), push-ups, burpees, planks, crunches, squats etc. Many to do, only issue is you have to make them intense after a certain point to get a good workout.
Here is a link to some DIY strongman equipment, Ive made some of this and it works well. There are similar ways and the exact things don't always need to be used.
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Homemade gear link: Its all cheap and there are some GREAT ideas in this thread such as the water ball etc.
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And just youtube search stuff like "odd object lifting" etc and Im sure you'll get some more ideas! Really anything heavy can be used for weight. If you need any help working out let me know, Im sure I could help you.
For your diet Stick with your complete protein foods(lean/red meats, fish) but if you eat incomplete proteins(plants, nuts, peanut butter) than compliment them with another incomplete protein such as bread or more nuts. Remember to take a break 1-2 days a week and after 3 weeks take a week off, idk if you plan to do intense training or not, might be a good idea. Really just try to eat healthy. Most people suggest if you want to build muscle to get 1g of protein per body weight but you don't really need that much if you try to get buff but if you want to get strong you will need more than the normal person. For example if you weigh 160lbs and you want to get stronger then getting 120g-140g would be fine and still help you build muscle.
Food to eat:
Lean meats such as ham, chicken, pork chops etc for protein
steam veggies -if you STEAM them they maintain their nutrients
Fish -tuna, salmon and so on
Chicken
Eggs
Milk
Tuna
Protein Powder
Ground beef
Just eat anything with protein, carbs and low fat
Foods to avoid:
fast food
junk food
bad food
food with corn syrup /processed
JUST BECAUSE ITS FAT DOESN'T MEAN IT WILL MAKE YOU FAT! Sat fat in healthy amounts from meats, nuts etc will help produce more hormones espically testosterone which will then in the aid of building muscle.
If there is ANYTHING else please let me know I am sure I could help, I know this is a lot of stuff but Im sure it will help you and really it was no problem.