Here is mine. I didn't make the flag. I put MAIL in felt letters on the side using felt glue and I used Velcro to close it with. I also used the fabric I used for the bike baskets.
I also made envelopes following this tutorial, and made removable stamps using this tutorial. Here are other cool projects I found, Here, Here.
I LOVE the fabric combinations, I especially like the blue flower and dark blue combination.