Surface flow - depending on the conditions, it might be possible to hike to surface flow. Inquire with Kalapana Cultural Tours.
Ocean entry - At the present time, there are three ways to access the area where lava is flowing into the ocean: (i) walk the approximately 10 miles round trip over the county emergency access road from Kalapana (you can also walk over the road from the National Park side as well) - UPDATE - you are now restricted to .5 miles from the surface flow due to dumb tourists putting themselves in danger and almost getting killed. As a result, viewing ocean entry from land is not as enjoyable as it used to be; (ii) rent a bicycle from one of several companies and ride to the ocean entry; or (iii) pay for Kalapana Cultural Tours (www.kalapanaculturaltours.com) to drive you most of the way and then hike or bike the remaining approximately 1.8 miles each way.
Lava Ocean Tours - The owner of Lava Ocean Tours has been reported to be reckless and it is recommended to take a boat tour with Kalapana Cultural Tours instead.
Caves/lava tubes
Thurston Lava Tube (parking now restricted to 30 minutes)
CAUTION: after SCUBA diving, wait 24 hours before going up the mountains
Mauna Loa
Mauna Loa Observatory - if this interests you, contact MLO to arrange tour; they'll ask, "you know we don't do astronomy, right?"; will give you code to gate; one-lane, seriously winding and undulating road
Kalapana/Kaimu - black sand; 10(?) minute walk over lava rock
Punalu'u - black sand; good place to see turtles (I once saw 4)
Papakolea/Mahana/Green sand beach - there is a local family that shuttles folks from the parking area to the beach for a nominal fee. Private tours can also be arranged to the beach and surrounding area.
Hapuna - has been rated #1 in US, top 10 international
Greenwell offers free coffee farm tours and free tastings. Bring your own milk/cream/sugar - http://www.greenwellfarms.com/
NPS sites
If you plan on going to more than one NPS site in your time in Hawaii, it probably makes sense to get a Hawaii Tri-Parks Pass, which costs $30 per year for all three parks that collect fees (HAVO,HALE,PUHO), instead of up to $25 for a few days for one park.
Mauna Loa Macadamia Nut Visitor Center - skippable; more expensive than Walmart; Rabbi Chazanow, previously of the BI has said that nuts without any chocolate/dairy are PAREVE, including Dry Roasted and Honey Roasted, even when bearing the OU-D
Hotels:
Kohala
Kona
Volcano
Hilo
Getting Around:
rent a car
Harpers - only rental car company that allows you to drive anywhere on the island