There are so many possible variations on this! Add your favorite picture from the trip. Add little trinkets, a postcard, ticket stubs. a twig or a rock from a hike:
Label them with tags or press-on letters:
These would look so nice on a bookshelf or next to a bed. And, collected over the years, they'd look so lovely as a group. A perfect way to create a beautiful and instant memory.
Have a great day!