How much food do you cook for a dinner party?

You can technically peel vegetables days ahead, as long as they are stored in either a Ziplock bag, a Tupperware, or other airtight storage container that will keep them from drying out. Some vegetables will keep longer than others, depending on moisture content and how long is has been since it was picked. The main thing to remember, though is that even if the vegetable looks okay, the vitamins in vegetables will start to degrade as soon as they are exposed to air. So in terms of the health benefits, the longer the time, the less appealing it is. Minerals and fiber benefits, however, do remain.