We visited Haleiwa on a Monday and hit no traffic. There was ample parking around - there was a shopping plaza where we parked and browsed around, and walked up and down the street. We didn't find much in terms of shopping. We had lunch at Kono's which was amazing - one of my favorite places we ate at all trip! Its just a quick service spot with picnic table seating. We stopped by the shrimp trucks around 11:30am and it wasn't very busy, just decided not to eat there. I'd also recommend visiting Matusomoto's for shave ice. If you want a nicer sit down dinner place, Haleiwa Beach House is great as well.
We didn't go as far as the Bonzai Pipeline where the surfers are. We did stop at Laniakea Beach which is between Haleiwa and Waimea Valley to see the sea turtles. Its a quick stop with parking across the street, but that can be challenging. It also can be challenging to get down to the beach for anyone with mobility issues.