Jeeze. All kinds of stuff actually. I was a kid really, but immediate memories:
1. Ride bikes around, see if friends where home and go build jump ramps or build forts in a vacant feild.
2. Make a fishing rod from a stick and see who could catch a fish first in the river with it.
3. Play cards, betting some embarrassing or physically difficult thing you had to do if you lost.
4. Ride/walk into town and check out the shops, pawn shops and local ice cream parlor. There was always some trinket shop too that had neat stuff no matter where we lived that I’d go routinely explore. Pawn shops where also a favorite, got my first guitar from there and outfitted my first car’s stereo with speakers from one.
5. Build or dismantle something to do whatever I wanted it to do. One summer I got tired of being on bunk beds with my brother and the trailer park we lived in had a bunch of left over 2x4 wood in a random feild. So I built him and me two separate twin beds. Then took apart the old metal bunk bed and built a treehouse with it sometime later.
6. Head over to a friends and play video games or sit and watch a movie together.
As an adult, I wondered a lot. Would go on hikes or explore new parts of the city I was in. Internet at this time was around, but not as apart of daily life as it is now.
I’d wonder and stop in at a bar, call up a friend and go do something. Often it was us all doing things we needed while also just hanging out together.
Come to think of it, socially speaking, things where much, much more social back then. Additionally, there was always a presence of whimsy or seeking to be inventive. With either your time or with you time+ whatever resource you had. I.e. a whole weekend on paydays would involve bars and buying things to mess with.
It was just a constant effort to invent something to fill your spare time with. Very often involving one or two buddies hanging around too.