Have attendees hide a small wrapped gift say with in 1 Mile/Km of the event location, marking down the Coords.
Have them put the coords in a cammo'd film can, along with a log inside it.
All the film cans go into a stocking , now have a flash mob event and, and everyone who hid a gift, draws a film can.
Taadaa, you now go out and find your gift, and as a bonus you have a ready to hide micro cache as well.
Later on have your main event, this is where you open your gift.
If for some reason you could not find your wrapped gift, you stand up, show your film canister, and hopefully the gift hider can go help you find it.