Probably been thought of already, but I thought I'd bring it up.
The old Alice style 1 qt canteen cover has a pocket for water purification tablets. I carry Micropur MP-1 tablets in them currently, but I noticed this pocket was also the perfect size for one of the spark lite firestarting kits. Seeing as how the rest of the canteen cover seems awefully underutilized, I was thinking about adding a few more pockets.
Perhaps one identical pocket on the opposite side that can carry something like a spark lite firestarting kit, and maybe a larger central pocket that can hold an altoids tin, space blanket, bug repellant, or whatever one can come up with.
What do you think?
(haven't added pockets yet, just stuff for size reference)
Nalgene seems to be the trend lately, but I like the alice connectors since you can hook them up to any belt (not just the web gear) and even just the waistband of your pants if you aren't wearing a belt.