If you think about something you want in the glistening room, it appears. The glittering sparkles on the wall come down and coalesce, leaving behind something similar to what you were thinking of.

If you think about a pepperoni pizza, you might get a pizza with pickles on it. If you think about a nice tall glass of water, you might get one, but it's really bubbly! All of the food and drink from this room is edible and potable, unless you're wishing for something else. There are also potable sources of water throughout the caverns (not the cistern, though, don't drink that).