We have two great ones for our Tricky Tray! The first is lunch for one kid and two of their friends with our Chief of Police - he'll pick them up/bring them back in front of the school with sirens and lights going.
The other is a consultation at your home with a reputable garden/landscaping guy from our town's nursery. This guy is great--people are always bringing him bugs, diseased leaves etcetera to see what's wrong with their flowers or trees, so to have him come to your yard (he doesn't do this normally) to see what any problems are and tell you how to fix them is something a lot of yard-freaks (like my husband

) would kill for. He's been trying to get the lawn of his dreams since we bought the house over ten years ago and has almost succeeded a couple of times, but the grass just never seems to hang in there.
We made these two special prizes for our town's residents only.
We're still trying to find an in with a fire department to see if we can get them to host a birthday party--we'd supply the party supplies in the basket, what we'd like them to do is give a ride (if liability issues allow) on a fire truck, slide down the pole, do games like which kid can get the equipment on the fastest, roll out the fire hose the fastest, that sort of thing.
Good Luck!