I have a junkyard about a mile from where I work. I've been detecting for about 10 years. From 2004 until 2010 (7 Seasons), I just kept my coins and other items that interested me.
I wish that I would have kept everything with current metal prices.
Since 2011, I have started kind of separating my finds. Still keep the coins and other interesting items separate, but I have buckets for Aluminum, Brass, Copper, and Iron/Steel.
EVERYTHING that I don't know what it is, just gets throw in with the Iron/Steel.
Sure Iron and Steel is only maybe 9-12 cents a pound a times, but it adds up. Aluminum, copper, brass, and lead are all much more. It isn't hard to dig $50-100 a year in scrap metal. Some people probably get a lot less, but I'll guarantee you some get a lot more than that. It could pay for batteries, gas, or a few good meals.
I started a separate Savings Account when I started detecting. My goal was to put all my Clad in there until one day I had enough to buy something awesome. Now, I also put the money I find in there from Scrap Metal (found when detecting) and pop cans/bottles found when detecting. My goal is to have enough one day to buy a Springfield M1A National Match. If someone asks how I could afford it...I'd simply state...Digging Pennies!!! HaHa.
Of course, my problem is that I don't dig much Clad so it doesn't add up that real fast.
Either way...one day maybe I'll enough to get one.
DH24