Our day in Hilo was for me, actually the best and most organized. we only had around 6 hours and wanted to go up to see the Volcano National Park (http://www.nps.gov/havo/index.htm). Before the cruise I had rented cars in every port. I will tell you that this was both a good and bad experience and I definitely have some recommendations.
Originally I had rented all our cars through Hawaii Car Rentals (http://www.hawaiicarrentals.net). They are a rental consolidator that allow you to book all your rental cars for all the islands on one website. Looked great. So I booked. Got really nice pricing and an e-mail back from them that said, "Please e-mail us with any questions. This e-mail address is monitored by a human." Well that human must be asleep because every time I would e-mail them for info I NEVER heard back from them. Finally I got so fed up I cancelled all our cars with them and rebooked them. I am really glad I did. For instance, on Maui they had us going all the way to Maui's main airport (Kahului Airport) to pick up our car. We found out from the folks who we rented a GPS from (more on that later) that we should not take a 45 minute drive in each direction (in a cab, on our own dime) when we are going to pick up and drop off the car. We ended up renting (with the other company) at Lahaina's small airport, only a 10 minute shuttle away.
There were other problems but suffice it to say we were NOT happy with them. We were happy with Discount Hawaii Car Rentals. (http://www.discounthawaiicarrental.com) They do exactly the same thing but they do it with GREAT customer service. Even after Celebrity changed our itinerary which forced us to rebook all but one of our rentals, they were OUTSTANDING! I would definitely use them again. They were totally responsive and got us great deals on our minivans. That is not to say that all was perfect on the rental car front. Just on booking them. I will cover that later as I get into each island.
Getting back to Hilo, we arrived on time, thankfully we were docked and not tendering so we took the shuttle to pick up the rental at the airport (you could see the ship from the airport, that's how close it is) and then went back to pick up the rest of the group and headed off to see the volcano. Our rental car that day was from Thrifty at their airport location and they did great. Quick pickup, easy drive, plenty of people at the agency to check us in and a clean, good looking mini-van ready to go.
Kilauea was much more interesting than I thought it would be and we ended up seeing a bunch of the volcano as well as a walk through a lava tube and we finished the day with a quick stop at the Mauna Loa macadamia nut factory. Strange that they call it a factory. I thought nuts were grown, not manufactured.