For low spots you need something like soil or sand which has permanent volume. Compost and manure are organic and will completely disappear in a year or so leaving zero residual volume.

Bare spots don't necessarily need soil unless they are low and hold standing water after a rain. It is best to determine why the area is bare and work on, or with, those conditions.

For compost on a lawn 1 cubic yard, not 2 cubic feet, is normal. A bag is 40 pounds. A cubic yard is 700 pounds.