Congratulations!
About 20 years ago, we started collecting little items from our travels to hang on our Christmas tree. Now, every year when we decorate our tree, it brings back fond memories of our trips. Our kids are now grown and travelling on their own, and they have started doing the same.
I find a lot of souvenirs are kind of ticky tacky. (Diamonds and gold aren't, of course, but those are beyond my budget.) I don't mind when tree decorations are a little bit kitchy, so this works for me. Also, these don't take up a lot of room in our carryons, since we don't travel with checked baggage.
We try to find items that both appeal to us and are representative of the places we've visited. If we can't find an actual ornament, we find keychains work well, also, and other small items can have a hook or string attached or glued onto them. For example, we have a "cornament" (beaded cob of corn with deerskin leaves) from a pueblo in New Mexico, a little Eiffel Tower from Paris, a red lantern from Hong Kong, a Grace Kelly and Prince Ranier medallion from Monaco, a little streetcar from Lisbon, a bull keychain from Madrid, a miniature Gaudi lizard from Barcelona, a maple leaf made from part of the old Parliament roof from Ottawa, a miniature stein from Munich, a tiny "Sisi" plate from Vienna, and so forth.
If you are someone who observes Christmas and puts up a tree, perhaps something like this would be an option for you. It would be great to start off the collection with your honeymoon trip.