D.J.
I see someone beat me to suggest the "Win It In A Minute" type games.
Another idea, and this is not an activity, but I read in a magazine (possibly Family Fun) to take a photo of each house and give the neighbors a button to wear with the photo of their house on it. That way you can match faces with the homes.
Waterballoon tosses, bean bags, tug -of - war, 3 legged races can all be easily set up without a lot of prep work.
You could have a limbo contest too. My kids had fun trying to spit watermelon seeds at a picnic recently. Have fun and good luck!