Humans would certainly have had famine or feast as part of their every day experience. I believe the idea of occasional gorging and extended fasting is worth exploring. Like you said kill a mammoth and everyone eats like crazy before the meat goes off or is stolen. Spend a few days sleeping off the excesses and go hunting again. For Northern Europeans (like me) fruit would have been only seasonally available but gorging on blackberries sounds like fun. Plains Indians would make pemmican with fat, dried buffalo and blueberries ground up together and this would sustain them for most of the winter. You wouldn't pick a fight with one either.