The following Everyday Savings Tip comes from, Pat:
I reuse envelopes. I just put a blank label over the return address and write on the ones that have the clear windows or put a label on the return address too! I then either glue or tape it closed and then mail it.
I always have blank labels from sending off for free samples and if you got your address on those free labels that come in the mail when people are asking for donations you can use that as the label covering the return address.