Not necessarily collecting, but track building.

I was in one of my local library's reserved playrooms with my kid, and they had a track kit. We played with it for a while, I showed her some of what I used do with them when I was her age.

2 weeks later, we have nearly 50' of track, a ton of stuff I printed in the last two weeks like clamps, jumps, turns, starting line, finish line, 5 new cars I bought, and just dug out some of the cars I had left from when I was a kid.

Halp! I'm spending all my $$ at Dollar Tree and Walmart!