Legos. Lots and lots of Legos.
Also, building toy guns out of scrap PVC piping, broomstick handles, and finishing nails. Playing "war" around the house with the toy guns we made.
The kid down the street picking 50 almost-ripe oranges off of our only orange tree, and hitting all of them down the street with a baseball bat.
Riding my bike 20 miles to the beach.
Going to the pool nearly every day for 10 years, growing up surrounded by people my age wearing almost nothing, and later in life wondering why most of the country acts like a bunch of puritans when it comes to showing a little skin.
Joking around with the kid who got a speeding ticket at age 14... on a skateboard... in a 25mph zone.
Winning the school "bike rodeo" in 5th grade with a perfect 100% score, and getting an hour's ride-along in a real cop car for a prize. We didn't shoot any bad guys but man were we ready!
Not having enough money to stay in hotels on vacations, so twice a year we went camping for a week in one of our national forests. Wondering later in life why some people freak out when they're out in the woods, and teaching USAF survival school using things that I learned at age 8 during those family camping trips.