What would you be looking for when traveling for a souvenir?

I collect shot glasses (small glasses with picture of where it was from) when I travel.
BUT...the best idea I've heard of when travelling to a lot of different places is to buy two postcards. On the back of one, write down funny stories of what happens, or a list of what you see and do in that place, and who you meet - things you want to share with family and friends when you get home.
On the back of the other one, write your own personal memories, thoughts, reflections - things just for you to keep as a memory from your trip to that place.
The best souveniers are small, inexpensive, and will remind you of the place.