I got in on the DL deal a few months ago and will be spending 6 days on Oahu in May. The one activity we splurged on is Pearl Harbor. My kids are very excited about that.
We are looking to spend minimally on all other activities (hotel is on points and still looking into best rental car prices). We will spend some time snorkeling at Hanauma Bay which looks to be a very inexpensive activity. We are also going to drive up to North Shore and explore the beaches and hiking trails that lead to waterfalls or swimming holes that will hold the interest of my boys.
We are also going to look into getting a few of those foam boogie boards for hours of fun at the beach.
I am pretty certain I can keep activity spending at a minimum. My worry is the cost of food.