What does smouch mean?

The word smouch (which is pronounced just like smooch) is apparently an American invention. It's a bit of slang that means steal. It isn't very commonly used, in literature or speech, though Mark Twain seemed particularly fond of it. It appears in The Pickwick Papers, Roughing It, and a few times in Adventures of Huckleberry Finn, as in this example:
"Now, there's SENSE in that," I says. "Letting on don't cost nothing; letting on ain't no trouble; and if it's any object, I don't mind letting on we was at it a hundred and fifty year. It wouldn't strain me none, after I got my hand in. So I'll mosey along now, and smouch a couple of case-knives."

"Smouch three," [Tom] says; "we want one to make a saw out of."

Twain also uses it in The Tragedy of Pudd'nhead Wilson:

They would smouch provisions from the pantry whenever they got a chance . . . ; and so far were they from considering such reprisals sinful, that they would go to church and shout and pray the loudest and sincerest with their plunder in their pockets.