So, I am really "into" the hobby of genealogy, and I have a cigar box full of mementos and the like that belonged to my great grandma Anna, that my grandpa Eric (Anna's child) gave to my mom in his will, and as the family genealogist, I have it.
Inside, among many neat things, is a a postcard book. Now, I obviously love postcards. Add genealogy and wow! These cards are from Anna's husband (also named Eric) from when he, with the "rainbow brigade" fought in WWI in France, before he was gassed (and hospitalized, and lived). These are from about 1918. Almost 100 years old. So not only are they "cool" because they're old, vintage, collectable, but they are a family heirloom, my great grandpa must have brought them home with him or mailed them to his parents, so they have sentimental value.
My pictures of some of them are terrible because I did not want to bend the book of cards or touch them for very long so I took super quick, ugly shots but I think even then, they are beautiful.