I have this happen to me in a restaurant once. I had no issue with it.
No problem, tiffanee is right. The food waste in this counrty is off the charts.
Imagine how many people could be fed just from what goes to the dumpster of every grocery store each week.
It's be more admitable if he was giving it to a 3rd party to have something to eat. More and more restaurants and other food places are giving their left overs (that haven't been served) to homeless selters and other things like that (which is also smart, because if they track it they could get tax writeoffs and other such posative items for food they would of thrown away).
A coworker was invited to the manager's house for dinner. She said after everybody was finished, his wife would take everybody's plate and eat all the leftovers. He sadly admitted that was true. I never had dinner with him, so I did not get to witness that.
My mother has an extreme aversion to food waste. She came up during the depression. She tries to get me to freeze....everything.
If he is taking it home for his dog, no problem. If he is taking it home for himself, take a rain-check if he invites you over for stew.