I have the large Triumph tail bag. It fits all my gloves, water bottle, glasses, etc in it and is very high quality. If I'm just doing an overnight, that combined with my Triumph saddlebags is fine (I have an SE).
For longer trips, like the one I'm taking mid-September, I'm going to use my Route 66 T-bag. This is a fantastic bag, with tons of room, lots of compartments, and get this, rollers and a telescoping handle for wheeling through the parking lot up to the hotel. It's a bit spendy, but you won't regret it. You can also attach a top roll to it. My wife rides her own bike, so I usually end up carrying all the luggage.
Hope that helps,