You're already packing everything you own. This is a great time to assess and reduce your overall amount of stuff. Here's a quick look at how to triage as you pack and the options for where stuff can go if it's not going with you.
Keep or Cut (or Maybe)? - It's one of the major time traps of moving to get lost in old memories. Nostalgia is nice, but we've also got a job to do. As you're packing have a way to sort items into three categories "Keep", "Cut" or "Maybe". Have clearly labelled boxes/bags for the "Cut" and "Maybe" in a central location. Have separate boxes/bags for the various categories of items to cut (see below).
The Rule - Make a quick decision - will you keep it or cut it? - and if you can't decide in less than a minute - toss it in the "Maybe" pile. Come back to the Maybes later and re-sort them into Keep or Cut. A day or two or even just a couple hours later and you'll likely have a better perspective. This is totally personal preference - some people want to be surrounded by memories and others want nothing but the bare essentials - a spork and a hotplate. Some questions to ask: have you used this thing in a year or two? What would happen for me to really need this? Could someone else use it more often? Holding on to four pairs of pants you haven't worn in four years just in case you "paint the garage"? Ahem > cut.
Storage - for the stuff you keep, often there is another useful decision to be made: bring it to the new home or put it in storage. Storage can be a great solution for situations where space is at a premium. Especially if you have seasonal hobbies (skiing, badminton, leaf collecting), or any stuff that just doesn't get used more than every few months.
Second Life - for the stuff you cut, there are five major options:
Your turn - let us know in the comments if you've got anything to add. Thanks for reading! Here's to happy moving!