A pen pal is a person with whom you communicate with, usually from a long distance. Items can be just about anything. So, I guess it means items pertaining to a pen pal. It is hard to say without any other information.

A penpal relationship is often used to practice reading and writing in a foreign language, to improve literacy, to learn more about other countries and life-styles, and to make friendshipsAs with any friendships in life, some people remain penpals for only a short time, while others continue to exchange letters and presents life-long. Penpals come in all ages, nationalities and cultures. Pals may seek new penfriends based on their own age group, a specific occupation, hobby, or select someone totally different from them to gain knowledge about the world around them.A modern variation on the traditional penpal arrangement is to have a keypal and exchange email addresses as well as or instead of paper letters. This has the advantage of saving money and being more immediate, allowing many messages to be exchanged in a short period of time. The disadvantage is that the communication can be very ephemeral if the email messages are not routinely saved. Many people prefer to receive paper letters, gaining the satisfaction of seeing their name carefully printed on a thick envelope in the letterbox. Using postal mail, it is possible to trade coupons, swap slips, postcards, stamps and anything else light and flat enough to fit inside an envelope, often called "tuck-ins". Many penpallers like to trade sheets of stickers, notecards and stationery sets. you can find international penpals quickly and easily !

pen pal means pen friends so i think pen pal items are items sent by mail