Metal is always worth money.
Basic way to start is to grab a magnet and separate the piles into ferrous vs. nonferrous. Ferrous material is anything a magnet will stick to. Granted you have to have a large pile of ferrous metal to make it worth your trip but the beauty is ferrous metal is easy to acccumulate and doesn't require a lot of separation or preparation.
As for the other materials, I would separate them by type (chairs, grills, fencing, etc etc) then run a quick search on the forums here to see how to break them down. There is a lot of good information here which can help your overall return.
Cheers.
Tom
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