My rig - I have two handlebar bags in this picture. Both are Gille Berthoulds and are sort of expensive. I normally only ride with the black one, but this was for a double century and I needed the second to hold the battery for my light.

I keep food, money, cell phone, spare contacts, chap stick in this bag.

I have a small bento box which holds whatever I'm currently eating and another chap stick.

The saddle bag, that you can't quite see in this picture, holds tools, a jacket, a buff and short fingered gloves.

None of that answers your water bottle question, but it does show you what a small handlebar bag looks like.

V.