It seems like takeout food always comes with sweetened carbonated soft drinks, but this doesn't have to be the case. Diet sodas and unsweetened tea are almost always available, and at some restaurants you can opt for tasty low-fat milk. Sorry; the ice cream float's off the table.
You can be fond of takeout food and be eco-friendly at the same time. For example, don't throw out all the extra stuff you find in the bottom of the takeout bag; you can use those napkins, utensils, and straws for other purposes, so set them aside until you need them.