There are still times when I need to move small tangible items over long distances. In those instances, I turn to the United States Postal Service. Here are a few bits of the USPS code that I've cracked:
Using forever stamps means that you don't have to worry about small postage increases, and can even be used on heavier stuff. One stamp = one ounce.
How many ounces is that letter? Use a kitchen scale to find out!
For international shipping, a small box or padded envelope sent via First Class is usually cheaper than the flat rate fee.