You can get creative here, but you need some kind of loop/handle to help get the bottle in and out, as it'll be a bit snug. Maybe incorporate a carabiner, that'd be neat. Or perhaps leave a long loop of cord with a cord stopper/lace stopper/barrel lock/slide lock (or whatever that spring/button thing is called).

For the desert camo cozy, I made 2 loops. To do this I did:

*CH 3, SL ST in 2nd stitch from base of chain (this should make 1 loop).*

SL ST in next 3 stitches.

CH 3, SL ST in 2nd stitch from base, fasten off (this should make the 2nd loop).

For the red/black cozy, I made 6 loops to make it look kinda like a flower (this one's for my wife). I just repeated the step between the *-* above 6 times, then fastened off.

There are 12 stitches across the top, so you can make loops in any multiple of 12 and still have it look symmetrical. For you math-challenged folks, that means you could have 2 loops, 3 loops, 4 loops, or 6 loops.

I'm not sure how most people fasten off when crocheting with yarn, but for this project I thread the cord through one stitch, then cut it off. Then I carefully melted the end, and squished the still-soft molten plastic with the edge of my scissors to sort of mushroom it out.