Easy Print Bicycle Bottle Cage
https://www.printables.com/model/1610720-easy-print-2-piece-bicycle-bottle-cage

I printed "Camelback water bottle cage for bike" by theprintalot, and it works pretty well and is easier to print than some of the 1-piece bottle cages, but there were a few things that I wanted to change.  

I don't like multi-part print files, so I have uploaded the 2 parts as separate 3MF and STEP files.  

I beveled the edge on the bottle cage opening, so that it's easier to replace the bottle.  I also rounded off the corners.  The mounting surfaces where the screws seat was very very thin, I almost tripled the thickness of that so that the bottle cage is less likely to get broken off.

I simplified the other part, which I'm calling the "Mount Bracket," to remove a couple sharp edges, make it less fragile, and to make it so that it will lay flat on your build plate.  I reduced the counterbores on the backside after breaking one at the screw slot on the bottom, similar to what I did with the bottle cage part.

I works well with 21 ounce Camelback Podium Chill and 21 ounce Camelback Podium bottles without insulation, as well as a cheap sports bottle I got from work.

You can probably print both parts without supports if you have your bridging settings squared away, but tree supports won't hurt.  Both parts should be oriented properly when you open them in your slicer -- the cage should be printed with the beveled opening of the cage facing up, and the Mount Bracket should be on it's side.  The filament that you use should be something that won't soften when exposed to sunlight or left in a hot vehicle - basically any rigid material other than PLA.  I printed in PETG and ASA with 50% Gyroid infill, 2.4mm wall thickness (6 walls with a 0.4mm nozzle, or 4 walls with 0.6mm nozzle), and 2.4mm top and bottom thickness, which is working for me.