I've moved 6 times in the past 3 years. Fortunately, they were all in the same city.
The PO Box is a great idea, and I will do the same thing when I move again this summer.
I'll be moving outside of the country and it is a huge pain in the ass to get mail forwarded to there, so I think it is easier to have the PO and have a friend collect it every now and then and then either pick it up from them, or just pay to have it FedEx'd to you.
I'm curious what to do with my shit - I have a lot of random things that either won't work in another country, or are just too big to bother with. Like TVs and computer monitors and random furniture and baseball card collection.
I guess I will just sell most of it, but I'm not looking forward to it.
What I really have no clue of around here is throwing things out. You can just leave a couch on the curb here. Although I might drive to apts that I used to live at which had dumpsters and just ditch the things there.