Sadly, I find the current design water bottle section on my Tri-Star to make it pretty much a useless appendage on my beloved bag. I just don't carry a water bottle for travel--at least not in my bag where a leak could wet clothes, documents or electronics!
I have tried putting documents in there, but the weird tilt-out bottle pocket doesn't make it easy to insert rectangular objects--they just don't go in easily with the shape of the internal tilt-out liner and the curved zipper.
I've also stuffed small electronics in there, but they have a tendency to poke or fall through the loophole between the snaps of the internal tilt-out liner, making opening the zipper a quick way to drop some small chargers/plugs/adapters/cables.
There are a number of ways to fix this that I can think of:
1) add another snap and cut the liner all the way to the bottom so that the tilt-out inner pocket can be disabled entirely
2) change the snap(s) to a zipper that goes the full height of the pocket, so that the tilt-out inner pocket can be disabled entirely
3) replace the water bottle section with a regular, rectangular 3D compartment (give up the water bottle idea completely)
4) change the internal tilt-out pocket to some other system of restraining a bottle, like flat loops (not a great idea though, because inserting/removing the bottle will be a pain)
5) build the inner bottle pocket into the inside of the lid of the section, effectively turning the section into two pockets behind one zipper
6a) build a flat document pocket behind the bottle water pocket whose zipper is lengthwise along the shortest edge, from top right corner of the bag to the bottom right corner (ie, this section becomes two pockets with two zippers)
6b) build a flat document pocket into the lid of the section, in front of the bottle pocket, with zipper that goes from the top right corner of the bag to the bottom right corner OR just along the top edge of the section, from the top right corner towards the middle of the bag
7) change this section to a modular system that accepts an optional bottle holder pocket; without the bottle holder, it is just a plain 3D rectangular compartment (basically, a fancier version of 3) above)
Of these, I like the modular system in 7) best or 6b)+2), which would give me a flat document pocket and a 3D rectangular compartment behind it.
Anything to give me back use of that section of my Tri-Star (or Western Flyer)!