You'd be surprised how much room removing the saddlebag liners adds...I was. With just you going, you won't need to do that, but when there's two of you, it makes a big difference.
Like Spydy said....think like you would if you were carrying the weight on your back. I backpacked a lot, so got really good at getting by with as little as possible. If you've got it on your back, you'll start cutting the handles off your toothbrush to save weight.
I use waterproof stuffsacks made by Outdoor Research to keep things like rainsuits, fleece jackets, etc in (again, a holdover from my backpacking days). Available at true backpacking stores, in a miriad of sizes/colors to help organize your stuff. Cost from 10-20 bucks....not cheap, but will last you forever and are high quality items. Stuff sacks are great...just don't stuff 'em till they are tight as a football...leave some room and they will fill up corners and crevices better, you can bungee them to practically anything, and the OR brand has daisy chains (nylon loops on the outside of the sack) to run the bungee through, so there's no way for it to fall off...also has a 99% waterproof closure.
The bike is sort of the same...you need to think about how much weight you're putting on it. The Gross Vehicle Weight of our bikes is not as much as you think it is. The exact number escapes my feeble brain at the moment, but it's somewhere around 1350-1400 lbs. 900lb bike wet, rider and passenger can EASILY add 300+...that doesn't leave a lot of room for additional weight. Keeping the heavier stuff as close to the bike as possible helps in handling as well. If you've got stock shocks, be sure and check the air in them if you're going to load the bike. 15-20 lbs is minimum...when two up and loaded, 30+ is needed to keep you from bottoming out on hard bumps. Better yet, get rid of the POS shocks and put on something better.
The first trip or two, you'll carry too much stuff and not even wear it all, but you'll get it down pat after a trip or two. Training the wife/girlfriend is another story...
