Stow-on-the-Wold works surprisingly well without a car if you plan the day around the Market Square and the short walks that branch off it. The town is compact enough to make that realistic.
Arrive, settle into the square, then explore Sheep Street, Digbeth Street and the nearby lanes at an unhurried pace. A car-free visit is at its best when you let the town's compact scale do the work for you.
The point is not to cover every lane, but to see enough of Stow that the place feels lived-in rather than merely photographed. That usually means coffee, one good wander and time for a proper lunch stop.