I have a corollary: when I head out of my apartment/hotel/whatever, I assume I could be gone for a night or two -- you never know what will happen! This doesn't mean you need to lug around a bunch of stuff, but just enough basics to make it so you can easily say YES! at forks in the road that might require you to walk too far to get home that day, or stay overnight on a boat, or be out very late with a new group of friends. A toothbrush, change of underwear, and warm cost-thing, sunscreen, etc. Optionality is easy to prepare.