The sack inside a box of wine, the U.S. equivalent of a goon sack in Australia. Most wines now come in plastic bags, but most used to come in silver sacks. As a verb, "to silver sack" means to drink directly from a silver sack, usually as someone else holds it above your head.
(as you have a silver sack raised over your buddys head at a campground)
"Dude, that Allman Bros show was awesome! Silver sack it!"