1. Do you have a ziploc bag they will fit in? Then organize them later when you can do it in stages and get less overwhelmed?
2. Just do it in stages. One part of the room at a time. I always end up just putting one part of a room in and writing on the outside of the box what it contains, rather than trying to go through organizing it all into categories. I once had a box that said "alarm clock, leo tolstoy, pads, ear plugs, can of soup, etc" No joke. Then when I unpacked I'd just set up my room the same way, and if anything was left over I didn't want to put in the new room, I would just throw it in a catchall box, or throw it away if it was unneeded and not donatable.
Good luck! Keep taking breaks if you have time, I will be here all night and will try to keep an eye on this post if I can help with anything. I have packed SO many times it has even become fun at this point, so I hope I can give some good advice.
Edit: You know what? I didn't clarify if you were packing to organize, or to move? If it's just to organize I would still use the same technique, just box or straighten it up, and whatever you don't need and won't use again, either recycle or dispose of.