To be fair I think that's a bit harsh. You're only 17, you're still at school, you shouldn't be having to give up your money (unless your family's a bit stuck for money at the minute, in which case I suppose it's reasonable for your parents to want any help they can get - but if you're not in financial troubles, I don't think it's fair).
I always think I'd be seriously peed off if my parents expected that from me - they bring you into the world, you're not an adult yet, they should still be looking after you, it's their job!
Maybe if they were insisting you contribute to things you buy, eg. clothes, cds or whatever, or if they made you pay towards things such as your car or extra-curricular activities that would be ok. But for necessities? Food? That's a bit tight!