Probably more space than content. There would be milk for cereal, soft drinks, sport drinks in several flavors, bottled water, and several cartons of fruit juice packs. By the end of Season 6, or into the summer, there would be beer for Spike, which Giles and Xander would pilfer whenever they felt like it.
Solid food would consist of various types and ages of pizza, and in Season 6, leftovers from the DMP,( assuming that the stuff didn't self destruct at dawn like dead demons do), maybe some cold cuts and cheese to go with the stale bread on the counter, an assortment of fruit, and, of course, several nearly empty condiment bottles and jars, and handfuls of little catsup, mustard, and BBQ sauce packs left over from burger runs.