Whatever you want to call it, barf bags will catch it. But they can do so much more. From airplane hacks to terrestrial everyday uses, airsickness bags are more versatile than the world gives them credit for. And they're free.
Step 1: Store leftovers
Airsickness bags are lined with plastic, have tabs to seal in the freshness, and fold nicely. You can surreptitiously stuff in all the bread you couldn't finish before the appetizers came. Or carry home the soup of the day. The same properties that hold in food post-digestion can also hold the same food prior to mastication.
Disclaimer: using barf bags from the seat pocket on an airplane for food storage might be sort of gross. People do put their filthy tissues in there (among other things), and I can't imagine that those pockets get a thorough wash very often. It might be a little like eating off of a hotel bedspread. YMMV. I know a woman who swears by barf bags for storing leftovers who has yet to get sick.