Stuff you need if you want to send a letter on the go, or just feel suddenly inspired: airmail envelopes, beautiful short-run letterpress stationery, hand-painted cards by local artists, unique postcards, sealing wax and seals, and boxes of matches. Stamps of course, washi tape, pens, pencils, stickers, and all kinds of other snail-mail-esque goodies. Maybe some vintage postcards and vintage used stamps, and possibly even some good snail-mail related books.
I'd restock my vending machine regularly, changing up the stationery and card options so that passers-by could always find something new and beautiful to send to friends and lovers and pen-pals.
My vending machine would stand somewhere unexpected, like the street-art-covered wall of a laneway beside a cafe, or under the pavilion of a park, or inside an art gallery. It'd be pretty fun, don't you think?
* Inspired by this snail-mail vending machine, spotted at an airport (a much more sensible location, I admit) in Taiwan