I would ask if the time down at the beach is mounted or ground work. Most natural horsemanship "people" use a rope halter for ground work and a 12 foot lead (slightly longer than a 'regular' lead). But you can use a web halter, no big deal. A rope halter gives more precise signals to the horse and is harder for the horse to lean on is all. Some also use either a plain snaffle, some other bit, sometimes they ride bareback, or sometimes use a bosal with spurs for work mounted. Tack is very user defined so don't worry about that.
Do what your horse is most used to if she's going to be in a new environment. I would bring both a halter (if you will be doing ground games), a lead, a training wand/stick/medium length whip if you don't have sticks..., a longer line (a lunge line is fine), use a rope halter if you have one, your regular bridle, your saddle/pad setup. If your horse has never seen waves, you may just want to be on the ground for that.... Hehehe.... most horse need time to adjust to that and will spook/explode as the waves chase their feet.