Look, honey, he thinks there's honey in there!
We can't all be Zheleznogorsk.
What happens when you run out of food tokens? We supplemented discarded cards to mark the food we should've received and ended the game after the next turn. (Note: We also forgot to draw new cards for extinct species traits so that may have played a role).
In the rest of the Evolution Game System, food is meant to be unlimited; though the manual doesn't explicitly state it, I don't see why that wouldn't be the case here as well. In the Base game, you can substitute a wooden population or body size cube for 10 food tokens in someone's bag to 'make change'. For this game, we just used Go stones. You could do 10:1 with pennies or any other sufficiently different token in your bag.
Does a scavenger continue to eat even if all of its population is full? Or can this only be achieved with Fat Tissue?
Eating is a keyword in this game and means to perform the Eat action, which is to take food tokens from a source (Watering Hole or Excess Food pile) and place them on the Food spaces on the back of your population cards.
Scavengers eat one food every time a Carnivore eats until all of their Food spaces are filled. Fat Tissue is the only case where a species may take more food for a species than the size of its population. You fill the Food spaces on the back of your population cards, starting at the top and working down.
If I have a species with 2 population, Long Neck, and Fat Tissue, after the two eat from the excess food pile, can one of them then eat that third token from the excess pile because of Fat Tissue?
2 population with Fat Tissue effectively gives that species 4 Food spaces. Long Neck will place two food on the printed Food Spaces on your population cards, working from the top to the bottom, and then the third food goes into the 'extra' Food space on the top population card.