The North Shore is no longer the sleepy, hippy, world-class surfing meca that it used to be. It's like Venice, California, with a lot of tourists wanting to see the "sleepy, hippy, world-class surfing meca". There are even some really good restaurants/bars in Haleiwa ("The Gateway to the North Shore") that add civility. But remnants of genuine Winter Surf may still be around when you're there, so be careful going into the water above your knees if the surf is up because of rip currents. The "Must-Be-Done" thing in Haleiwa is to get a "shave ice" from one or the other of 2 roadside stores toward the north end of town. These snow cones have been a tradition among North Shore goers for decades. After a day at the beach, they are heaven. I recommend that you include the special instruction: "Put on lots of syrup and stop just before it falls apart." Then you will have a snow cone that is tender and flavorful all the way to the bottom of the cone.
And forget about Sand Gravity - there is too much to see in Hawaii for you to want to squandor your time zonked out with a drink on the sand. Besides, I think liquor is illegal on a public beach in Hawaii.

About the Hawaiian Sun - sunburn is a real threat. Use 30+ sun screen with UVa/UVb protection and re-apply if you perspire. Even put it on the tops of your feet (tourists always forget that and get sunburned feet).

Have Fun! And know that you'll be going back again.
~Reggie~