What I usually keep is the food that's left over :)). It's normally non-perishables like salt, sugar, pepper, sauces, jams (in small packs) well and tissues... Also, fruits like apples and pears.
All of those normally carry airline's identity, like logos and stuff... similar to sickness bags. :)
Then it's nice, someday, to take out a, say BA's sugar and use it for your tea, when you're in Eastern Siberia, Russia :). (that's where I live, and do that when I get "Britain-sick") :).
Scotland - Russia.