Some of you make this sound complicated....
Scale: Take a guess at the weight, you'll be close. If you are a little over and have to pay the difference, it might cost $2. You'll have it perfect for your next shop. I'll spend the $2 up front before I buy a scale..
Mailing Address: My work is in a different zip code from where I live. If I do a post office shop from outside my zip code, I just mail stuff to myself at home. If I do it from the same zip code as I live, I just mail it to myself at work.
Boxes: You have some variation in boxes. I have not had to buy a box - I found four or five at home that I was just going to toss. I wrapped them with paper grocery bags and was good to go. When I want to do another shop, I just tape a piece of paper over the previous post office markings (or peel off the stickers) and mail the same box to myself again. I have four boxes ready to be mailed now and am expecting another delivery today. I hope to mail one again tomorrow.
Hard work builds character and homework is good for your soul.