Sources:
Spring to autumn - forage underbrushes. It’s a lot of food once your survival skill gets good.
Winter - pine nuts and boiled acorns. Hard to get by, but not undoable.
Heavily mapgen dependent: insects and spiders - easy to kill, but semi-rare, unless you come across an anthill
Special preparation needed: river - you need swim goggles and a speargun and you need to drop a lot of stuff before diving (or you won’t be able to breathe far from land) but there’s just SO MUCH FOOD in there
Luck-dependent: sewers - rats, snakes and fish there are tasty and easy to catch because they don’t flee
Preserving:
Winter - stuff rots very slowly in winter, treat normal food as if it was almost permafood
Jerky - needs cooking 3 and salt or salt water. If you’ve got a swamp nearby, salt water is free. Otherwise try to make it using seasoned salt. Easiest to make permafood.
FOODCO rig - ultimate food preserving machine. Slap it on a car and you can dehydrate stuff pretty much for free.
Cooking:
Carve a skewer from wood (use a knife on a wooden object). They don’t take space and don’t weight much, but they allow cooking meat (like pointy sticks).
If you have enough mechanics, fabrication and survival (about 2 each), make a quern and mill acorns and buckwheat into flour. If you can get your hands on some cooking oil, you’ll be able to make biscuits that have AMAZING nutrition value for their cost (28*8=224 nutrition just for 2 flour and 1 oil).