Dumpster diving for food. There's a LOT of waste food out there in the dumpsters behind grocery stores.

I read about this in a book called "The Art & Science Of Dumpster Diving". It was available through Paladin Press, I got their catalog for a while many years ago. They had all kinds of books that today would probably be unpublishable. Many of them are available through annas-archive.org.

Anyway - it was never an absolute necessity, but it was always a blast, like treasure hunting, never knew what you would find.