Right now I carry a 12oz Gatorade bottle with custom mix. (I drink a separate 12oz bottle about 20 min prior to HM event.) What I don't like is that it's difficult to drink out of on the run (twist cap off, tilt head back, recap), and that I could use about 16oz. What I do like is the thin bottle, and the upper grooves provide an easy grip. The 20oz Gatorade bottle is too large for my preference.
All the "sports bottles" down at the sport stores are HUUUGE.
I tried a 16.9 oz Aquafina water bottle + a flip cap from a 24 oz Aquafina water bottle -- but the flip cap is hard as heck to snap, and their bottles are made of such thin plastic now, eww, crunch crunch crunch, it's gotta crinkle and leak eventually.
Something like this possibly:
But with the "reduced diameter" just above middle for grip, not at the bottom.
Any suggestions?? (ps. no water belt suggestions please.)
edit: ha, I went down to REI and found that 16 oz CamelBak bottle ... it's larger than my 20 oz CytoSport twist-cap bottle. I found a nice 16 oz Clif Quench twist-cap bottle though, that'll do -- nice finger groove and it's the same diameter as my 12oz bottle. Most bottles are 16.9 oz / 500 mL not the slightly smaller 16oz. It makes a noticeable difference, amazingly. I'll just deal with the twist-cap or hack together a custom cap and straw ...
Just Do It!