There is a town up there called Haleiwa that has lots of shops for browsing, and also a popular shave ice place called Matsumoto's. I would recommend checking surf reports closer to the day you are going to the North shore, the waves can vary a lot by the day, so some days you'd see 6ft waves, others it could be 15ft, the surf report will also help you to know if it's a good day for surfing, if you want to watch the surfers.
One beach I have really liked is Haleiwa Alii Beach Park, it has one area that is more calm (over to the left from the main parking area) and ssshhhh one of my favorite places to see sea turtles in the afternoon after about 2pm or so. More to the right/straight ahead from the parking area I often see surfers and some of the bigger waves.
One popular place to take a picture would be next to the Haleiwa sign on 83, if you are coming south toward the turnoff to Haleiwa. (sorry, not sure if that is a great description of where it is...)
Another would be at the shop close to the bridge, Tropical Rush (I think?), there is a painting of what looks like angel wings on the wall, you can take your picture with that...