This is another case of myself. I made a square card similar to this a week or so ago and decided to make a 3 x 5.5" version with an envelope. I used the new Modern Label punch from SU--I love it! Pattern paper is October Afternoon Cherry Hill. I'm really stuck on this Life stamp set but I'm proud that I didn't use any Kraft or twine on the card.I saved the twine for the envelope (insert evil laugh here). Here's the front of the envelope. I used the twine to hold the flap closed but ribbon would be equally lovely or a belly band of some kind. Hopefully I won't forget I made this for my sister since her birthday isn't until November. This is not for the sister I give a hard time about her age. I have 2 sisters.
For an envelope to fit this size card... start with a piece of paper 8.25 x 6.75. Score at .5 on each side. Rotate and score at 2.5 and 5.75. Trim away some pieces as shown in the picture and use Scor-Tape(or something similar) for the adhesive.