Chalk it Up!  Kids can play with chalk for DAYS!  At least mine can and what a way to get their imagination going full-speed.  My kids play four square, big tic-tac-toe, hopscotch and other classic old-fashioned games.  But I think their favorite thing to do is to make their own big neighborhood.  I love when they make their own neighborhood complete with street names, signs, and ride their ride-on cars.  Nice day out, we love to have a carwash with soapy water, buckets, and elbow grease.