Here's my biggest suggestion. Committees and sub committees!
We have a Fall Festival at the elementary. We have games, a supper, King-Queen, Prince-Princess Ceremony, Cake/Prize Walk, and Basket auction. The biggest thing is the haunted house.
Start with an overall committee to see what direction you want to go with the thing. After that I would form sub committees. Not everyone will be interested in doing the same things. Donations and getting sponsors were always the hardest for me to get volunteers for, I hate that myself. Games, their locations, and prizes must be figured out. Signs should be made. Make sure everyone has in-kinds and keeps up with the donors for "thank yous."
In the past we have done crafts, the kids can buy them or donate them to sell at the festival (usually for .25,.50, or 1.00). This has been a big hit. Other booths that have been popular are the toilet paper toss, tatooes, face painting, and hair coloring, fish pond, wheel of fortune, quarter drop, guess how many (candy corns or something in a jar), lollipop tree and duck pond (for the smaller kids), ring toss (kids try to ring a soda bottle) and basketball toss.
Our KQPP contest is over 50 years old. Since I've been around we've never made less than $10K. The supper does well too. Since we have it in late October the basket auctions and prize walk are popular because people use those for Holiday gifts. In the past the talent show was held after the KQPP ceremony. Our principal felt there was not enough attention on the performers because so much was going on and also it did often go pretty late.
