Cover Swap

In philately, the term cover pertains to the outside of an envelope or package with an address, typically with postage stamps that have been cancelled and is a term generally used among stamp and postal history collectors. The term does not include the contents of the letter or package, although they may add interest to the item if still present. Cover collecting plays an important role in postal history as many covers bear stamps, postmarks and other markings along with names and addresses all of which help to place a cover at a given time and place in history. (depict from Wikipedia)

For this cover swap, you can use either one of the following:

1) A series of matching stamps (must be more than 3 stamps of the same series or same theme) on the envelope

or

2) A first Day Cover (send inside an envelope)

or

3) A miniature sheet/souvenir sheet on the envelope

In the envelope, you can put a postcard or a notecard.

Have fun swapping beautiful cover.