"What is that one or two pieces of gear you only carry for a zero day?"
Nada, zip, nothing. Zero gear for zero days. In the places I visit, simply wandering around experiencing the "unbearable lightness of being" provides all the enjoyment I could possibly ask for. About as SUL as it gets. Actually, I have always allowed for a substantial number of such days when planning my trips. It is a major reason I go to the mountains. Some go to pick 'em up and put 'em down; I go simply to be. Diff'rent strokes for diff'rent folks, I guess.