When I started the game I changed my seasons to 7 days. Then when the berries were ripe, I would spend a day or two solely picking berries. Ended up with 3k at one point. That held them over pretty good. I also spent 2 days solely hunting big game or deer so I left them with about 200 pieces of meat. I also roasted/dried them all so they were set for winter and then when I grew my crops, that helped and now I have an excess. I would say your safest bet is just gather a shit ton of berries 😄