there's also the question of which store(s) to go to. I need more stuff from two stores that are farther away, but the need for stuff from the closer store is more urgent; and since I don't have a car, buying things at one store and then dragging them through the second (or third) store is unappealing. :| plus if I were to hit all three it would definitely mean I'd have to take the cart, which isn't fun in the rain. growf grrf.
(although I usually don't mind it, sometimes not having a car really is that much of a pain in the tail)