I have already searched and read many things.
We will be in Kauai 2 days off of a cruise ship.
We are renting a car on day one and going on a helicopter ride on day 2 and then back on ship.

On the first day, we want to drive to a few waterfalls and then spend the rest of the day at a beach.
We are looking for a beach with some waves to use a boogie board (we have 2 kids), a place near to get a few drinks and maybe some lunch. Possibly a place to rinse off. Clear water...
We think we want to choose between Hanalei Bay or Poipu, what do all the experts say?

Pali Hali (sp?)...fantastic beach!!

Either end of the Na'Pali coast - both beaches are awesome. If I had to choose, I'd choose the beach by Waimea Canyon (which is also awesome!)

If Pumpy means "Polihale" in the west, be aware that the conditions are generally not favorable for boogie boarding. There are strong rip currents and hazardous surf. The beach is beautiful, though very isolated. None of the other "amenities" you seek is near. You might try `Anini or Hanalei up north, or, as Amaclise suggests, Ke`e, at the end of the road, where the snorkeling and scenery are very good.

Since you mention:
We are looking for a beach with some waves to use a boogie board (we have 2 kids), a place near to get a few drinks and maybe some lunch. Possibly a place to rinse off.

...either Hanalei or Po`ipu would work just fine. Personally, I'd recommend Hanalei Bay -- with a stop along the way to tour Kilauea Lighthouse. You'll probably want to do this on Day One -- drive time from our harbor to Kilauea (non-stop) is about one hour, and Hanalei is just 10-15 minutes beyond that.

Have a _great_ time! 8-)