The first things I included were these little sticker sets, which have about 5 stickers each to decorate the letters. I put them in small plastic bags and folded pretty paper over the seal. I stapled the paper to the bag to make it look nicer than just a plastic bag.
I also included 5 envelopes, 5 folded pieces of graph paper, 2 stamps, and 2 erasable pens. I would have included 5 stamps, but I didn't have enough on hand.
In this picture, you can see everything I put in the kit. I also put pink and white stick on rhinestones, and a few paper flowers.
It all fit nicely in a pencil box.
I decorated the pencil box with some stickers, and also put each person's name on their box. I put a post it note on it in the picture to cover that up. I made a 3x5 card that says "Let's Be Pen-Pals!". Before I give them away, I'll tie a ribbon or string around it.
I think this is a super fun gift to put together, and one that would be fun to receive! I hope to do more posts in the future about pen-pal ish things too.