There are many different options. One option would be to get one of these clip-on bottle holders from Cascade Creek: Yakuzzi - Cascade Creek. This would be a quick, easy, and affordable solution. Another option would be to attach a more permanent gear-mounting system like this one from YakAttack: MightyMount II. Then you could mount a cup holder like this (YakAttack MultiMount) onto that attachment point. If you have one of our Caribbean kayaks, then you could mount that YakAttack cup holder to the accessory tracks on either side of the kayak too. These are just a couple of suggestions but you can get as creative as you want.