I found them on Pinterest (where else), followed the links to the original post, and this is my first crack at making a couple of them. Guess what: they're super fun.
You just take a 9-card baseball card holder, mine are from Staples, and fill up all the pockets with goodies for your pen pal. Each slot is 2 ½" x 3 ½", the same size as Artist Trading Cards (ATCs). NOT the same size as your Project Life cards. Those are a majestic 3"x4" and won't fit in here.
Anyway, these were for people who like very specific things, so they were easy to create. The first lady likes fabric, sewing, stickers, buttons, lists and gum. Those are sewing needles, by the way.
The second lady loves her garden, used stamps, stickers, tea, band-aids, buttons, and things for gift-wrapping, hence the twine. Oh, and sparkly things. You probably can't tell by the pic but the star card stock and a few of the buttons are pretty glittery. Hopefully she'll like it.
I wasn't sure how I was going to cram a proper letter into a single tiny pocket but I did figure out a way. I folded a piece of card stock in half, then added 3 sheets of onionskin paper, also folded in half and stapled in. Because the card is so small I was able to use my regular desk stapler for this, no special equipment required! The paper is nice and thin, and although I didn't write a novel-length letter or anything, at least I was able to say a few things.
If you're careful about how chunky all your items are, you can fold the card holder into thirds, because it fits perfectly into a business size or #10 envelope, and then mail it off. It'll likely be heavier than a regular letter, so you might need to add more postage. But if you don't make it too fat, you won't have to send it as a parcel. Hooray!
If you want to send bigger items, then this format may not be for you. But for a novelty, it is kind of cool.
Now, go make something!