It also depends on how important the characters' gear and equipment are to play. In a game where gear and equipment are carefully tracked and-or can be vital to success, forgetting to pick up something while in town can have big consequences later and thus at least doing the basic "adding items to one's sheet and knocking off the requisite number of g.p." step is rather important.
A recent example from my game: the party found themselves in a null-magic zone in some caverns. All their magical lights went out, and most of them couldn't see in the dark (lots of Elves, and in my game their night-sight only works outdoors). Much checking of character sheets later, it turned out not a single one of 'em had a mundane lantern or torch to provide light! Someone did have three basic candles, which were used to get them through to where their lights came back on.
Next time in town they all loaded up on mundane light sources!