Everywhere I have been in the world there have been lots of "foods of the world" shops/aisles/sites and lots will have relatives that drag things here and there. Being the experimental sorts I imagine we all give things a punt from time to time and well "? million people can not be wrong" is often applicable to food. Take away type things can count but try to avoid them if you can as such things are usually "? with a ? twist". Naturally things you discovered on a trip can count in this.
My absolute favourite has to be lemon and passion fruit juice, I got it when wandering around Amsterdam one morning and it was delicious. I have not been able to find it since (and I visit every shop I can) so I can not reasonably add it to this list.
I will go through a few points in time where I like Kvass (a fermented black bread drink reasonably common in eastern Europe and Russia) but I do not seek it out.
There are these cherry biscuits similar to Jaffa cakes (I think they are Polish) that I will occasionally buy a pack or three to munch on the way back from the supermarket.
I will also take foods you miss when you visit somewhere else (squash when I visit the US. I can deal with the sub par bread, I can deal with the awful cereal and though it has effects very similar to withdrawal I can even give up salad cream but the lack of squash gets to me).
Comments along the lines of "of all the things you like ?" and "kind of amusing that I could go down to the corner shop and get hundreds" as well as things you get asked to bring somewhere/back also play.