Bottle holder - aluminium or titanium bolts?
i always avoid aluminum fasteners wherever possible due to a lot of bad experiences with them disintegrating over time (especially nipples on fancy wheels), but i'm not a weight-weenie, just weight-conscious.

i would say if you can afford ti bolts that'd be what i would go for, even though it's overkill and you'd be shaving maybe 1/10th of a gram. of course, if you were truly a weight-weenie, you'd leave off bottle cages entirely, right? ;)

if you're using this bike on a trainer, definitely avoid aluminum fasteners, as your bike is bound to be covered in sweat that'll accelerate the corrosion on the bolts. the things i've seen on trainer bikes.... disgusting. weight wouldn't be much of an issue on a trainer though so i imagine you'll be riding it in drier conditions.