Pick up the envelopes/etc from the mailers at a USPS branch office. There is a section in the store to buy things (the fancy boxes and evenlopes); but there is also the free ones used for 2 day shipping. Don't take dozens at a time obviously, but go in and grab a couple the next time you drive by. I'ver never had to pay for those envelops and I grab a couple each time i'm in there to do other business.