Sidewalk chalk is very inexpensive. There are SO many possiblilities when you have a sidewalk & some sidewalk chalk. Here are just a few ideas:
Hopscotch. I drew the grid & the boys drew the numbers. Preston traced the numbers that I wrote. The grabbed a "stone" from our rock collection. They played forever. I would say it was one of their favorite activities.
A letter game. I wrote a few letters on the sidewalk & just asked Preston to stand on the letter that I said. You could do the letter sounds.