If you’re traveling abroad on a tight budget with absolutely no extra room in your suitcase for a souvenir, then buy a stamp. Even the lowest denomination stamp of any country is colorful, cheap, and easy to find.
When you get home, mount the stamp in the middle of a piece of poster board, write the details of your trip on the back of the poster board, and put in an inexpensive frame. You’ll have a decorator look on a backpacker’s budget.