This drink holder reducer relies on the flexibility of TPU or similar materials. It is designed to be a tight fit but since I only have one car to test with, you might need to do a rescaling in the slicer to prevent it from coming out with the bottle.

As shown in the 3rd and 4th pictures you can flip it over to fit larger drinks which would not require a reducer. This way you don't need additional storage space for that part.

Print instructions

Print it in a flexible material, the open side should face up. Use 100% infill and enable the feature to not cross perimeters for traveling. Otherwise it will be pretty stringy.