Unfortunately, in 2009 they cut the schedule down to 1 movie due to funding cutbacks, but we went to all the screenings in December 2008 and it was great fun.
Food vendors are pretty decent and you'll find something the kids will eat.
Do bring jackets and a blanket/towel to sit on as the beach does get chilly fast.
A flashlight is also a handy tool / kids toy to have on this adventure.
Sunset on the beach is a lot of fun but like the other review said, make sure you get there early. Keep in mind sunset in Hawaii comes really fast so when they say the movie starts at 7pm, it means that the beach is dark at 7pm.
While the movie may or may not be the focus for the kids, the sand will definitely hold their interest. I suggest throwing in the sand toys and don't forget that this is right on the beach. It can be cold and windy, a little damp if you are on the ground (most likely the kids will be) and they are going to get full of sand. Unless you know the movie will hold your kids interested, I suggest moving to the water side of the screen, it is much easier to get out from here if you need to get the kids to the bathroom or if you need to leave early.
Make sure you take a trashbag with your cooler / diaper bag. This was probably the most important lesson we learned from our first trip. We didn't have a trashbag and the diapers were piling up. Yes, they have trashcans, but they aren't in the area where you are sitting most likely.
One other suggestion, I have several friends that enjoy taking their kids to the beach and then staying for the movie. I have done this once and discovered both of the kids zonked as soon as the movie started and I had a nice enjoyable movie experience without chasing the kids - however, if you want to take the kids to see the movie, and actually watch it, I wouldn't try to do beach in the same afternoon. I also would like to point out that the zoo is just adjacent to the beach where the screen is setup. Our easiest time at Sunset on the Beach was when we went to the zoo in the late afternoon, stayed until closing, grabbed out cooler out of the car (and re-fed the meter, which can add up to a pretty penny at $1 / hour for the zoo lot), and headed to the beach. The nice thing was, we had the stroller and were parked close. Lugging the stroller across the sand was a pain but it was so nice to have at the end of the night when both kids fell asleep.
A huge screen is set up on Waikiki beach where they play movies when the sun goes down, generally around 7pm. It's a lot of fun, but you need to get there early to get a good place to sit.
Seating is basically first come, first serve. Find a spot in the sand to put down a blanket and you've got your seat. Some people even pile the sand up to make back rests. You can bring your own chairs, but if you do I'd recommend the "L" folding chairs that have backrests, but no legs. Everyone wants to see the movie. =)
There are quite a few food vendors, but we usually bring our own coolers with food and drinks. Where ever you get your food, though, please remember to clean up after yourself.
The movies are usually family movies. That can be cartoons to movies like "High School Musical" to action movies.
It's a great opportunity to picnic with your family and watch a big screen movie. It's totally free (unless you buy food from the vendors) and the kids love it... actually, my husband and I also enjoy going without the kids as well.