I dont know if the Post Office will like you for this one, but these invitations have been wrapped in hand sewn canvas bags. The addresses and stamp have been printed onto iron on-fabric transfer paper (the invitations were printed on real wood!
How to make gift bags from newspaper. DIY recycled newspaper project: gift bags made from the Wall Street Journal. You can vary the dimensions, of course, but here's what I used to create a bag that's tall, wide, and deep.
Corina Nielsen Photography & Designs: Part 1- The new look!