Death wobble, or speed shimmy or whatever the hell you call it is a pretty mysterious condition that can be caused by a number of things. Weight distribution is indeed important, although I've found front loading makes more of a difference than rear. I'd try without the water bottle first, then ditch the clothing in back, see if that helps.
Oddly, sometimes more weight is the answer. When I attach my trailer, my bike has speed shimmy like mad, and my 'speed' I mean 15 mph. However, this goes away as soon as the trailer is loaded. Why? I haven't the foggiest, but at least now I know not to ride no handed with an empty trailer.