I've found that it's safe to stack boxes about 5 feet high, if they're tightly stacked. If you plan to move during the wintertime, include a box of salt, in case the sidewalks are icy at either end of your move. As you pack, set aside a couple of boxes for things you no longer need or love. Donate them to Goodwill or another charity. In doing this, you've done a good deed, and made your move a little easier.
Canned goods can go to the local food pantry.
Many charities will send somebody by to pick up your boxes if you call them, so making a donation doesn't necessarily mean more running around when you need that least. If you can afford it, hire someone to move your things rather than doing it yourself. Even if you think you can't afford movers, call around for estimates and calculate what the move will cost you to do yourself. The difference may not be as much as you think, and it'll be money well spent. You'll save a lot of wear and tear on yourself, and your friends will be understandably grateful.