I know this idea may not sound the best initially - but I've seen sleepovers at the school bring in big money at auctions. If you can convince several teachers (or principal), whoever, agree to all take a Friday and have a sleepover at the school, the highest bidder for that teacher gets to come. That way, the kids are with other kids and there are lots of adults to supervise. Teachers can provide the pizza.
Another idea is to bid on a "behind the scenes tour" of the school. The highest bidder(s) get to go into all the "off-limits" to students places. Like the staff lounge, the janitors' office, the teachers bathroom, the cafeteria kitchen - any place you can think of that the kids can't go - the highest bidder gets a peak.
And...I agree on the parking space - HUGE money maker - we do that for our baseball league. If parking isn't an issue - then maybe a "cut in front of the line at parent pick-up" is more enticing to some.
Some ideas I have seen a dessert a month for a year, an appetizer a month for a year, 3 dozen cookies around the holiday, a pizza and a movie with a teachers, teachers donate their time so parents can have a night out, a teacher takes pictures of your child throughout the school.
We are having a silent auction at our spring carnival and last year had goof success with what we called service auctions from the teachers. We auctioned off 'Principal for the day', 'Lunch with the Principal', 'Job Shadow', 'story reading', 'no homework coupons'. Does any one have any ideas that we could include? Any ideas would be helpful. We auctioned these off during a live auction portion and was a blast. Someone paid 75.00 to be Principal for the day. Thanks in advance for any help