Tracked in the wilderness, handwaved in civilized lands. (Deducting decent inn prices; if they want to save money and chow rations or hunt, I slow it down and they can either track or have a quick encounter.)
Sustenance can be a nice "danger clock" to build tension while adventuring - food in the arctic, water in the desert, sleep in a bandit-infested thicket, even air in a poisonous cave. But it can get tedious, so handwaving it in civilized lands gives a distinct impression of the differences. "You're in the Borderlands now, everyone start tracking food and water ..."