Is this wrong...please fucking say it is!

[crash]

You're in a locale where there's no heath ordinance against taking food that you own out of the establishment. There's more than you need on the plate.

Would you let it be tossed in a garbage bin rather than eat it later or donate it to someone in need?

Yes of course I would, on a few conditions;

It wasn't a shared meal where other people have served themselves from cutlery they've eaten from (I won't even eat seconds at a table where this happens, or first from a dish that somebody else has had seconds from).

If I can get it home and into a refrigerator reasonably quickly

If I liked the food in the first place.