>i am sure they recorded the second side of the tape but i wonder how dangerous it was
They were designed for that to begin with! Cassettes could reasonably fit 4 tracks of "passable" quality audio on them, which usually took the form of 2 sides of stereo (an A-side and a B-side, just like vinyl records) - this is how the majority of commercial audio cassettes were sold

However, you could also buy a 4-track recorder for amateur multitrack recording - this would give you 4 mono tracks that played simultaneously and could be mixed independently

>and there were metal chips with pictures in snack bags and kids would trade them
When I was a kid, we had Pogs and Tazos - they were mostly card or plastic, sometimes with holographic pictures. It's a little "culture shocking" to think there's people that didn't grow up with these

>there was also this game https://www.youtube.com/watch?v=X4FQmtFf5s8
That's called Tiddlywinks - usually it's played with little plain plastic discs that are specially made for the game, as seen in teh video