In Chemistry lessons me and my friend used to either talk about random stuff, play 'baseball' (i.e. used a ruler to try to whack shards of another broken ruler at the clock), continue carving through the desk with scissors, chuck balls of paper back and forth at other people in the class or, in practicals, get every single chemical in the cupboard and mix them together, topping it off with a sh*t tonne of universal indicator.
Yes, we were that bored. There are a lot of things to do if you're bored enough. Not so easy if you're sitting with someone you don't know though. In my last year of school though I cared so little about my other subjects that I spent every Physics lesson working on random maths problems I found online, which was fun for me but maybe not so much for non-mathematicians.