Help! I'm clearing out my room because I'm moving...?

I started taking all my stuff out of draws yesterday, and towards the end of the day I gave up. I HAVE to get it all in boxes and sorted by this afternoon because some people are coming to see the flat, but it's just so HARD! I've kept things from when I was younger and I know I should let go but I can't decide what to keep and what to throw. I know I'll have to chuck it at some point, so if I don't do it now I'll have another tough job the next time...please tell me something to keep me motivated or a way to make this less boring? And what should I keep and not keep? PLEASE HELP BEFORE I DROWN UNDER THIS MOUND OF CLUTTER!!!!!!!