well in the new episodes. Tales of a Leo, they have flashbacks of when they are all young...anyhoo Leo and Splinter were looking for other people's discared "junk" in the sewers. -Also in both the new toon (garbage man guy) and the old toon, the turtles have befriended the homeless. They've always been on the lookout for their nifty odds and ends.
Has for the food question: I think I remember specifically that in the old toon the turtles get money donated to them via Channel 6, for helping a citizen in need (the citizen wanted to make sure her heroes were paid), and April of course passes it on. It was at the end of the episode, since the turtles are psyched they can get PIZZA!
-Plus the turtles are resourceful, like in movie one, Mikey gets $3.00 off cause the pizza dude is late!
-Every little bit counts