Another option is the save the letters and use the opposite blank side to use as scrap paper. You can store them in a basket. They are handy for printing online coupons, printing directions, invoices after you order something online, and emails you want to keep in print form. I like to do sweepstakes and use them to print the official rules. Think of how much $$ you'll save from having to buy reams of paper.
I also use envelopes from junk mail to put my grocery list on or a "to do" list for the day. Sometimes I jot down reminders for myself.