I've done a 10,500 mile trip to Alaska plus three 2500 mile trips through the Southwest and Mexico, all solo on my S2R. I think all the previous posts have you covered pretty good. Here's what I have to add:
Earplugs- The moldable silicon kind are the best, you can get them at any drugstore.
Tank bag- Is great to rest on and to block the wind. As long as you're not putting multiple bottles of water in it it won't affect the weight distribution that much.
Camping- It'll vastly increase the amount of stuff you have to carry if you decide to camp out (tent, sleeping bag, pad, food, etc). Also, it's hard to know ahead of time what exactly you'll need. I'd say for your first long trip, don't camp out. Stay in motels. Most of the time you don't need to call ahead. Your credit card is king.
Saddlebags- Soft ones will probably sag so watch out for contact with the rear wheel.
Rain gear- For a seven day trip through the Southwest you might be able to get away with not having any, but if you're going to take that risk check the weather ahead of time. Also, insert a trash bag into the saddlebags before you pack everything in, because soft saddlebags will leak rain cover or no.
Comfort- I've used the stock S2R seat this whole time and it's never given me any trouble. You might want to consider handlebar risers but depending on how resilient your back is, you can do without them on a seven day trip. You'll also want a darkly tinted visor and good sunglasses.
Other stuff- Plug tire repair kit, chain lube, maybe a 1 gallon gas jug. A multitool would be useful, as well as a flattened aluminum can for the sidestand on soft ground (put it in your tank bag where you can reach it without getting off the bike). Eye drops are nice to have. A small container of rubbing alcohol is useful for many things (cleaning your visor or bike, disinfectant).
Tips- Always carry one more bottle of water than you think you might need. Also check the weather the night before for every place you might be in the next two days. It's never too late to adjust your route to avoid rain.
Things to avoid- At dusk, as the sun is going down, avoid the urge to rush to wherever your stop for the night is. Do. Not. Rush. The lighting is bad, other drivers can't see as well, animals come out, you're tired and your judgment is poor, shit happens. I can't count the number of times I've nearly crashed or killed myself when I didn't follow this rule.
Try to find out ahead of time if the place you're stopping for the night is particularly popular that night. There's almost no worse feeling than rolling into town, finding out that all the motels are full, and having no backup plan.
Taking the interstate will mean missing a LOT of things. A state route or smaller back road will take longer but will be richly rewarding. Avoid letting other people dictate your pace too much. The point is to have a good time, not make good time.
And in the end, experience is the best teacher. Fifteen months ago I was exactly where you were. You'll develop your own list of what to do and bring, far better than any list you read that somebody else wrote.
That being said, go out and have the greatest time of your life!
