I would go somewhere where a lot of people go like at a flea market or something like that and sell snacks and sodas. If you sell stuff like that where there s a lot of people they will buy what you got. Just have a sign that says what you are selling is for a fundraiser and that would help with any competition you may have
My family have done activities such as band nights (hiring out a club/pub and hopefully getting bands to play for free, it included raffles of gifts that were kindly given to us, tombolas and just donations), sky diving, bake sales, runs (my town does a 10k run every year) and just general things like that. You could always see if everyone will just chip in for the homecoming that way you won't have to pay extra money to do fundraising activities. My school did it once and announced it in assembly to see who was up for it. We all gave about £3 for it. Good luck!
Coupon books
You could go to local businesses and ask them to sponsor your homecoming.