Or you know, just eat half and take the other half home and eat it later. Of course, re-heating doesn't work as well with some dishes. I've found there are some places that would be too expensive for me and the only reason I eat there it because I can amortize the cost over 2 meals due to their larger portions; particularly if the food is re-heatable without a large degradation in quality. Think curries or other foods with lots of moisture.
I do when possible but I don’t always want to eat the leftovers again. But often we’ll be out and it’s just sitting in a container in the car and becoming increasingly unsafe to eat.
