Left over anything from a meal eaten at a restaurant is sad and gross. If you didn't finish it, it's garbage probably.
"Oh hey could I get some kind of box or whatever to put this little bit of food I have left on my plate in and take it with me to my house so I can reheat it and it'll be gross and not enough nom nom nom?" Like is it just a snack then? It's not a meal. I don't know. I don't care for it, though I do realize it is wasteful I suppose. Something about it has always put me off. No thanks I say even as a young gun.