Paddleboarding and Snorkeling - Both are a "must try." You can rent paddleboards and snorkel gear by the hour at Gary's "shack" at the Mauna Lani Beach Club. Look for the Yellow Tang fish, and you might even see a turtle!
Saturday Farmers' Market in Waimea - Every Saturday, from 7:30 am to noon, there is a farmers' market in Waimea called "Waimea Town" Farmer's Market - definitely worth the 30 minute drive up the hill to Waimea! Go there for fabulous crepes, fresh island fruits and vegetables, breads and pastries sold by the Sandwich Isle, and lots more! https://waimeatownmarket.com
Go parasailing in Kona
- Contact UFO in Kona for a great (and not so scary!) parasailing trip near Kailua Pier in Kona.
https://ufoparasail.net/kona-activities/hawaii-parasailing/
And after parasailing, make sure you get some shaved ice at the Scandi's ShaveIce,
http://www.scandinavianshaveice.com
Turtle hunting and whale watching - We see turtles often in the ocean and on the beach. From late December to early March, you also often see whales right off the shore. For whale watching, another option is to take a whale watching tour. We recommend Ocean Sports that leaves from "A" Bay at Waikoloa Beach Resort, https://hawaiioceansports.com