I have a bunch of stuff in my arsenal that I don't anticipate ever using. For example, there's pretty much all the gear you get from rank missions. There's a lot of stuff I can sell, but I'd only get a single crown from it. I was thinking of auctioning these items, but I can't imagine why anyone would want to buy them (despite seeing active auctions for these crap items in the auction house). Some items I am talking about include:
Hot Edge
Beast Bashers
Slime Slashers
Hatchets
Frost Gun
Robowrecker
Cold Snap
Firecracker
various low level armors and shields
By extension, is there a guide to working the auction market?
Finally, are there any good uses for minerals? I've read (vaguely) that if you sell them, it builds levels in the arcade, but the payback is pretty lousy per mineral (I've seen 2-3 crowns at best) so I've been hoarding them until I have a good reason to get rid of them.
I kinda miss the old times when people were depositing minerals with the purpose of creating the levels they wanted... Too bad this is gone now, it used to be a part of SK's gameplay and cooperation.
As for the OP's question, the only thing you can do with minerals is to sell them for the "lousy amount" (thought if you have 500 minerals of each color and you get 2 - 4 crowns per one, it's not THAT lousy).
And the best thing you can do with that "junk" in your inventory is either keep it or sell it to a vendor to get rid of them.