The habit to get into is have a non-bulky resuable bag that folds up nice and flat and keep it in a jacket pocket or some other location that's available when y

The habit to get into is have a non-bulky resuable bag that folds up nice and flat and keep it in a jacket pocket or some other location that's available when you're out and about; and to put the bag back in that place when you finish unpacking at home. Relying on remembering before you leave the house or whatever is much less effective, I think.