This is a great thread.
Okay. One, and this is going to sound incredibly weird, but my brother and I made… well, there’s no word for it. We called them slip-towers. The idea was to take a bunch of Fischer-Price wooden blocks and build them into a large (well, maybe three feet at best) tower with a shaft down the center, a bunch of twists and turns, a few dividing branches, and some output holes at the bottom. We would then drop in a Star Wars figure and see which hole it came out. (We liked R2-D2 best, as I recall. No arms, round head, he didn’t get snagged on any outcroppings. IG-88 was the worst… way too tall.)
Our house was on the beach in a bay on Puget Sound. We spent endless hours diverting muddy, rusty drainage water through a maze of channels much like the Sound itself.
My friend Mike Spencer and I usually commandeered a metal structure on the playground that was vaguely like a rocketship, and we had plenty of space adventures there with our fictional computer (who switched from being Vic, as in “Vic-20,” or Vincent, as from Disney’s The Black Hole). Whenever we encountered pools of acid exploring the Alien Playground, we usually encountered a pool of acid because Mike was so good at the sound effect.
My brother and other friends recorded radio-show-style adventures on a tape recorder, complete with primitive Foley work (shoes on hands, thump on side of desk). My brother also shot a lot of footage with an 8M camera, which, if you know my brother, can’t be too surprising. Ask him about it sometime. 
Oh. And my absolute favorite, Boggleshoe.
Boggleshoe was a game invented by Brent Swift, played with athletic socks. You can carry two socks. You may choose to wield one sock as a sword, and the other worn up your arm as a shield (blows against the shieldsock don’t count). You may also wield two swords. For a time, it was fashionable to roll up one sock and stuff it inside the other. Instant flail! But then we progressed to Socks of Mass Destruction with two rolled up socks as grenades. Arms and legs were one point per hit, body was two, head was three. Nine points wins.
FISH