If you donate to charities like the Cancer Society or the SPCA, you get packages of address labels as a thank you gift. I find you get a lot and they last a while.
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An easy, cheap, and frugal way to save money is to cut your name and address out of junk mail then shred the junk mail to use as packing material when shipping. Cutting your name and address out of medicine bottles labels is another way to save money and reduce paper consumption for return address labels.