I found your website when looking for suggestions on how to improve our school trunk or treat, and we do use it as a fundraiser. The NHS (National Honor Society) always sponsors it and we sell parking spaces for 5 pounds, along with food. Our school is a private K-12 school, so the high school typically runs food and occasionally a haunted house, and elementary school parents bring the cars and trick-or-treaters. There's a costume parade and prizes for the best car decorations which people always enjoy.
We also sell meal tickets for 5 pounds (the school is in the UK) and this includes a hot dog, veggies, a drink, and a caramel apple. This year we also plan on selling items a la carte as well as having more drinks and snacks like popcorn. Since its in the UK, its usually cold, so we provide a complimentary tea or hot chocolate or cider to parents who bring in cars.
In the past, the prom committee runs a haunted library as a fundraiser for that, with one pound entry fee, but this year we're changing it to some sort of pumpkin decorating museum. We may have carnival type games as well, which would be about a pound a game.
I hope this helps your blog! I love being able to find ideas online.