Herbal tea is ok and green tea should be fine, too. But you're right, coffee, Coke or alcohol should be avoided if you are short on water.

2 quarts per day might be just enough in a temperate climate providing that you're resting most of the time. When on the trail I know I need a little over a gallon per day to stay hydrated. Some persons might need less, some more depending on the build. In a very hot climate or in a desert environment this figure may easily double or triple, especially if you're engaged in a strenuous activity.