If you know any senior citizens they usually need help with everyday type things. My mother-in-law used to wait for us to come over to change light bulbs because she could no longer balance on a ladder.
The possibilities are truly endless. But you wanted a suggestion....so I would say, find something you enjoy doing, or rather don't mind doing, and put an advertisement in your local newspaper or on the internet (with your parents permission of course). Something else you might be able to do is go to a local nursing home or retirement community and ask if there are any residents that may need help with groceries/laundry etc.
My grandmother lives in a retirement community and they have people come in all the time to do jobs like that. Good luck :)