Here's a great bag that can either mount on the seat or the luggage rack:
http://www.harley-davidson.com/store/touring-luggage-systemBought this from a forum member end of last year. Was in great shape and couldn't pass up the price. Was actually wanting the Saddleman bag but again, the price was good on this one. It works great and expands as needed depending on the length of your ride.

A note on packing. I've learned a few tricks over the years. Pack your clean, old underwear and socks. Wear them for one day and throw away at night. No packing dirty items or having to worry about washing them on the trip or later when you get home. Same goes for old pairs of jeans. Plus leaves you room for items you may want along the way. Also, if you have a good vest with lots of patches or wear a jacket while riding, go by Walmart or any big box store and buy some cheap ($3-5 for a pack of 3-5), black (or your prefered color) t-shirts. Wear them for a day and leave them in the room/garbage can at night. It may seem like a waste but why wear a logo t-shirt if you are going to wear a vest/jacket to cover it anyway? And, if you dispose/leave it, no washing or packing of dirty items. If it's a rally or something you are going to, take a few logo shirts for those days. You can pack much lighter, get rid of items you were going to throw away anyway and still get one, good last use out of them. Food for thought....
