Check out Pinterest. There are literally thousands of great ideas there! Our Fall Festival included a nose picker game where the kids reached into our giant nose into some slime and picked out prizes. We also did a balloon pop, ball toss, a giant plinko game, cake walk, soda bottle ring toss, Wii dancing and auctions.
Here is my personal pinterest board with some ideas.
pinterest.com/paulettephelps/pto-festivals/
Papa Johns has large 1 topping pizzas in our area for $7/each, so we usually sell pizza at $2/slice, and set up value meal selections where they can get a drink as well. We ask for drink, chips, and 2 liter donations, as well as donations for the auctions.
One of our teachers did face painting, and it was a huge hit. Our vendors paid a small fee to set up the tables, but were required to donate an item for raffle. We had some great stuff for that!
A lot of businesses are always happy to help with donations. Check with your local realtors, and mortgage brokers. They usually have flexibility to make cash donations.