I had a lot of tribes die off b/c the game was still going on why I wasn't there and so the food supply would run out and wasn't able to replenish.

Pause the game when you will be logging off so that your people will survie longer. I haven't had any tribes die off since finding the pause button. Also use the Chief to replenish food so that if your food supply is empty, you people can still eat. Once your food supply reach 500, your people will stop worrying about food and stay to the task at hand. Hope this helps ^_^