Even though we took far less clothes than Roar1, I still took too many. I can never convince myself completely. BUT, I only took three pairs of shoes, and one of those was the slide-in type for airports. My feet are extremely narrow, so I can't get the hiking type shoes. I wear Easy Spirit AP1, in a tan buckskin; it fits securely and is flexible.
Ladies, forget jewelry and make-up, you either don't have time or are too tired to care.
By all means, take a jacket and gloves (and, unlike me, check to make sure you have a left and a right glove)! I like the driving gloves, then have a heavier pair to go over them if it's really cold; I can use my camera with the lighter ones on. I know I saw some people with the type that you can uncover the finger tips, but I didn't have those.
I took more battery chargers than I needed, but I'd probably do that again. I had several things running on AA batteries, and charged in shifts. I also took several adaptor plugs and was glad for that. I took a spare camera, just in case, that I didn't use. But I use point-n-shoot, so it didn't weigh much. I wish I had bought yet another camera, lusted after the one that the Webster's friend had with him. I'll be getting one of those soon. I also wish I had learned more about the camera I had with me before we went.
We used FF miles on Delta Biz. The seats are hard, but reasonably comfortable (I was dreading it since SAA's seats were really good), the pillows and blankets were very adequate. Food was better than I expected it to be, and service was reasonably good. We prefer to go all the way in "one fell swoop" and recuperate at the other end for an extra day, it just works for us.
And I agree with Anne, just look and enjoy part of the time. It's an amazing experience.