"paper sack" is a correct and usable phrase in written English.
You could use it in a sentence such as, "I put the groceries in a paper sack before heading home."
You could carry your stuff in a paper sack.
Stanley Turrentine carrying his axe in a paper sack.
I looked longingly at the paper sack of gin.
"You bring your own boots?" He held up his paper sack.
Then he reached into a bin and fished out a brown paper sack marked "Wise County greasy beans".
And a paper sack with his formula and his diapers and a tube of Polysporin for his belly button.
Ghosts and witches crossed from house to house, holding paper sacks and pillowcases.
These bags are not the big sloppy paper sacks you typically get at department stores.
They were holding cardboard boxes, plastic bags and paper sacks containing firearms and bullets.
School kids loaded with packs on their backs, Brawny laborers with food in brown paper sacks.
Also used are corrugated cardboard boxes lined with aluminum foil and paper or paper sacks lined with plastic.
