There are many things that you can include in your letters to your pen friends. These little extras are called tuck-ins because they tuck right into your envelope with your letter and should't use too much extra postage. Photos are probably the most popular followed by postcards are stickers. Below you'll find a few more.
Friendship books was probably the first tuck-in and then folks started to get creative. A friendship book was a little book, probably no bigger than an index card, that was comprised of several sheets of paper. Some are very elaborate while others are very simply decorated. They can be made specifically for someone or made solely for that person. The friendship book contains information on the person that it belongs to including the return address where the book is to be sent when filled. It is passed along from pen pal to pen pal and each person includes their name, address and some information about them like whether they'd like more pen pals or not accepting new ones as well as age. The last person to fill the last page sends it back to the person it was designed for.
A friendship sheet is basically the same as a friendship book except that it is made from one sheet of paper. Once again, it can be as simple as a piece of lined paper or elaborately decorated. The same principle applies, it is mailed back to the person it belongs to when it is filled.
Decos are like little art books. The cover is elaborately deocrated. On each page, someone adds their name and decorates their page. When the book is filled then it is mailed back to it's owner.
Lyrix and Quotz
These two are relatively the same so I added them together. In both a little booklet is created and decorated. In the Lyrix, folks add song lyrics. In the Quotz, folks add movie quotes. Both books can be completely random or they can be themed.
Slams are, once again, little booklets that are decorated. Each page is a question and folks have to answer each question. Generally there is room for names and/or addresses.
You guessed it! A little, decorated booklet! This one has no personal information in it and folks just basically "cram" as many names are possible in it.