I've touched on it in the "Side Hustle" thread and mentioned it a few other times, but I collect scrap metal and make runs to the yard three to six times a year.
Most of it comes from work. I'm at remote sites all week and it's equipment that's being retired from service and is destined for a dumpster. Typically, there isn't room to put one near each site, so I'd have to drive 30-80 miles to use the one at the shop. So, it rides home in the back of the truck and I use the time I would've spent driving to disassemble it.
Prices for steel and copper are down by almost half compared to last year, but it's still "free" money.
List as follows (in lbs):
Steel - 80
Cast AL - 420
Batteries (lead acid) - 185
Housewire - 6
Housewire #2 (tinned) - 19
Copper #2 tubing - 5
AL (clean) - 64
Stainless - 59
Low grade wire - 21
Transformers - 80
Burnt wire (oxidized bare/motor windings) - 5
All of these items were located in cabinets which are being re-purposed for use on my car/equipment trailers.
My other hobbies may not be very Mustachian, but I give myself a pass for recycling and in-sourcing. ;)