Make sure that you recycle envelopes that you receive from companies trying to get your business. You know the envelopes you get with "postage paid" on them? The ones without windows. Pull it apart, flip it inside out and glue the edges back down. I have a file folder in my file cabinet that I keep these envelopes in. As I am going through junk mail I toss these envelopes into the file and then maybe once every three or four months, when I have collected a bunch, I will take a half hour and pull them all apart, turn them inside out, and glue them back together again. Do it while you watch tv.
You'll never have to buy another envelope again.