Klark i was thinking exactly the same as you
Couple of flaws:
Bottle one, In most tests they make you take the label off
Pen one, There is literally nothing you can fit on that, and it's very suspicious if you're hiding something behind your palm, then quickly twizzling bak the pen
Rubber/Eraser one, so blummin obvious, if you saw someone turning over their rubber, i would be suspicious and ask to see their rubber/eraser, and a lot of tests give you your own pencil/pen/eraser/rubber
Paper one, The only slightly ok one, if the question asked you to write the formula, because you could say, the formula is: then just go over the words
Mostly they were rubish though