Google "motorcycle trip checklist". There will be a lot of people who have put these together and you can simply take what you want and forget other items but they do a great job of reminding you of things that may have slipped your mind. Then again, a credit card can get anything you forgot while you're on the road. I pack heavily but only because I like to be prepared. It relaxes me and helps me focus on the ride. My favorites:
Flat Tire kit
GPS (for gas stations and food) and a map of the planned route
Beaded seat cover
Clothes and such are pretty obvious. I've used the same bag setup as Surfndad above but since I've opted for no sissybar on the new Valk, I'll be using a large tailbag like the SW Motech tailbag or the Saddleman tunnel bag. Riding alone of course so the pillion is available for the bag.