A player perhaps starts the game with quiver (if they start with arrows) and a knapsack (i.e. backpack) but it can be useful to know what these items cost if these items needs to be acquired later in the game. Sacks can be a good thing to have to explain how you (or your horse) are carrying something. A horse can carry a lot of things due to its strength but you might need a couple of sacks to explain how it carrying certain things.
“I’d say thistles, but nobody listens to me, anyway.” - Eeyore