Pick 1 lens (if you have serveral) and put that lens on before you hit the sand (preferably before you leave the house, lol). I don't have any experience with beaches as I haven't taken mine to the beach yet, but I would NOT change lenses there. Too high a chance of sand getting inside and on the sensor and such.
I'm with Bree, in that if it's not around your neck, it should be zipped up inside it's bag.
Other than that, I think you should be ok. Don't dive into the water and you're set
