I REALLY like a tail bag... or a trunk as many folks call them. It just makes life so much easier for the daily commuter.
I bought this guy at JC Whitney for about $65.00 I know... I know... it's butt-assed ugly... HOWEVER... it does what I expect of it. And I like the fact that it is lockable and removable... so when I am touring... it can stay in the room if we make day trips. I have some plans to add something more substantial later.

Secondly for trips... I bought this guy from the T_Bags clearance site for $35.00. (Free Shipping! how awesome is that?!!) It is for an ATV but the smaller one fits the Valk perfectly... it had FOUR (count em!) water bottle holders. The two end bags zip completely off and have straps that make them into backpacks. Link here:
http://www.t-bags.com/CloseOutDetail.aspx?ID=69&SelectedCat=17
Browse through this gallery for more ideas about how all this fits on the bike... took these last week:
http://www.culleynet.com/zen/The%20Road/spring-ride-2011/