Interesting question. With ample solar, freezer, decent sized fridge, 500g diesel plus a watermaker and a compost head, limiting factors become food and perhaps beer/booze. Depends on what the underlying circumstances are. When 9/11 hit, my boat was equipped as a bug-out vehicle with 6-mos of very austere accommodations for two. For cruising? Depends on where we are. Gasoline for dinghy is probably our biggest hard limit. That and craving for fresh salad. Without that, we could easily go 3-months between provisioning if needed.
1970 Willard 36 Sedan Trawler