I live in southern California and bring my camera and lenses, including non weathersealed ones, to the beach all the time and have never had any problems.
And yes, I do change lenses all the time at the beach, just get into a habit of pointing the lens/camera down and away from the water when changing lenses as the mist/spray from the ocean does tend to get all over your stuff. To the same point, my front elements tend to be pretty covered in mist by the end of the day so make sure you have something to clean with.
I would also suggest you bring along a rocket blower or similar. Getting sand on your gear is pretty much unavoidable. I would take extra care that there isn't any sand around the mount when you go to change lenses. And NEVER wipe down any lens surfaces, even with liquid cleaners, unless youre sure that you have blown off all sand particles, youll essentially be sanding your lens.
As for being in the water while holding your camera, it really just depends on how comfortable you are with not dropping your gear and how high the tide coming in is. I have had my 6D and 17-40 on a tripod about a foot above the incoming tide level shooting a slow shutter of the water coming in. Camera came out unscathed but tripod wasn't as lucky, had to that it apart and clean every single piece.
Along with all that...ENJOY YOUR VACATION! Don't worry too much about your gear as everyone else said.
+1 I live in S Florida and frequently bring my gear to the beach, though I do try to use only weather-sealed lenses. I have to go at least once a year for the annual Air & Sea Show which coincides with Fleet Week. Though, sadly, it was greatly reduced to civilian planes & boats this year due to sequestration