Did you know that you can receive mail at any post office, almost anywhere in the world by having it sent General Delivery?
This has been incredibly handy for us while traveling. In the U.S. and Canada address the mail like this:
City, State, Zip Code
Then all you need is your ID to pick up your mail. In the rest of the world this service is called Poste Restante. For international addressing guidelines, see this Wikipedia link.
One challenge is timing. We’ve missed connections with our mail because it was late, or because we sent it to one place and later decided to go somewhere else. Tracking numbers are also handy. In Friday Harbor recently, I expected four pieces of mail and received only one. When I presented a tracking number for one of the missing pieces, all three magically appeared.