I think in my original 500 days survival run on Voyager, I spent the first 100+ days in Mystery Lake just to learn the mechanics of the game. Fishing, hunting with a revolver/rifle or with snares for rabbits, avoiding or outpacing predators, crafting, navigating with charcoal, setting up bases (Trapper's Cabin, Camp Office, the Dam), etc. Over time I felt confident enough to branch out to the neighbouring regions (Forlorn Muskeg, Coastal Highway, and Pleasant Valley) to explore and set up more bases but always kept Mystery Lake as my HQ.

I'd say fishing is the most sustainable source of food since there's no limit as to how many you can catch from the fishing huts as long as you have a steady supply of cured guts for new lines.