This bottle was once filled with stuff called "Vitamin Water," and I spooled a skien of white yarn onto a chopstick (I love chopsticks). The bottle is slightly larger and has thicker plastic compared to a regular water bottle. I cut the bottom and made a hole in the center of the base. When cutting the bottom, don't cut all the way around; leave about a half an inch intact to use as a hinge.
I bore another hole into the center of the cap, so the top of the chopstick could go through.
For more yarn to interchange in and out of the bottle, you could do this: