Photo-Caching (it may have a "real" name but that's what I call it] is where you could divide the boys into teams, and with either GPS coord's or a scavenger-hunt-like description, they have to bring back photos of the "finds". You can use simple things like "green car" and they would have to have a pic of one, some, or all of them with a green car. You could have coords pointing to a certain area landmark- say a statue in a neighbors yard (with permission) or a nearby bridge or stream- and a pic with the boys interacting somehow with the "cache site".
I was working at Wal-Mart a couple years ago and I was in the lobby taking my break and a group of girl scouts came in on a photo scavenger hunt. They had to have a photo of them playing leapfrog with a Wal-Mart employee. They asked, I consented, and they got the point.
So then back at the party, while the kids have cake and ice-cream, someone quickly downloads the photos, shuffles 'em (so that team one isn't all at the beginning and team 2 at the end), and runs a simple slideshow for all the kids to see. Photos could even be sent with the kids (or a photo-share site for the kids or parents to download) so that 20, 30, 40 years down the road the memories won't be forgotten.