Well, concerning the whole 'you may need to refer back to it' thing I think with the existence of the internet that's a null point.
You MAY want to consider keeping it for sentimental reasons - I'd personally find a year 10/11 and pass them on to them.
You can sell old books on ebay too.
I've just finished A-Levels - I gave my chemistry notes to my cousin because they're badass af but I've recycled everything else. It's just immature to set fire to it.