There is pretty much zilch. Each of the two terminal areas (which, annoyingly, you have to exit security to go between) has a bad restaurant, and a couple of gift/convenience type stores. There is a cafe where the rental car stands used to be but it seems to have quirky hours.

When I had a 5 hour layover, I rented a $20 car, went to Borders and had breakfast at the Big Island Grill.

With several redeyes late at night and no elite security lines, you'll want to make sure you allow enough time clear security, though.

As far as laptop goes, maybe you can get someone to let you in to the Hawaiian Premier Club. It's far, far, far from plush but does have a couple of carrels where you can work on a laptop.

I also know a secret for free wifi but you can PM me for that if you're interested