You guys didn't grow up watching all the old westerns that used to be on TV, or you would have known that expression immediately. I don't know how many times Gabby Hayes has said it! Never mind, you probably don't know who Gabby Hayes is either!
"Grub" is cowboy slang for food. like "I'm going down to the chuck wagon to see what kind of grub is for dinner"! So someone getting a stake for grub is essentially like a panhandler is nowadays.