There's a ton to do on the Big Island even with a lot of things shut down.

Generally the best snorkeling is right in Kona as some have already posted - taking a Captain Cook tour is great especially if you want to see dolphins or just going down to Two Step/Honaunau for great snorkeling.

Most of my family is from Kohala, so I enjoy going there. There's a nice hole-in-the wall restaurant in Hawi (North side of the island) - the Bamboo Restaurant and Gallery - great local food - even saw Ed O'Neill there once. You should also go see Pololu Lookout - there's a decent hike down to the black sand beach there. Mornings might be a better chance that it doesn't rain.

There are some great zip lines to check out - Skyline is the best one I've gone on - but looks like it's shut down right now. I would do that one again in a heartbeat- - we did UmaUma as well and it's was great - very beautiful waterfalls. I didn't like the Kohala zipline as much as it was mainly just in the trees and didn't have the views.

Hapuna is generally the best public beach on the island - it's not great for snorkeling as the waves are pretty decent for body surfing/boogie boarding. Next to Hapuna down the road is the Mauna Kea Resort - they hands down have the best beach on the island. They give away a certain number of public passes each day - if you get there around 10-11 am you probably won't get one - but check after 1 or 2 pm. The beach is great, and you can easily snorkel there as the waves are pretty calm. It's a little hike up and back to the parking lot but not too bad. - I highly recommend you at least go check it out...and they also have Manta Rays at night - and I've seen them during the day as well and also turtles are plentiful along the Kohala Coast.

Golf - There are some great golf courses - If you go to the beach at Mauna Kea - you'll pass the golf course there - it's pricy to play it but is an awesome course and you'll pass by Hole #3 that goes across the ocean (Google it..trust me) I think I hit about 10 balls just to get my fill hacks in. Hapuna has a great course. Mauna Lani - is also championship golf in the middle of the lava fields. Waikoloa also has two good golf courses. If you want something a little more affordable Kona Country Club is decent and has two 18 hole course - Mountain and Beach. Waikoloa Village is also a fun course -this is the course we typically play because our condo is right on the golf course.
Makalei Golf Course is also fun-and is more in the hills of Kona - but has some great holes and views from up there.

If you have some budget, Kilauea is fairly active right now - driving the Volcano is really an all day thing if you're coming from Kona. You'll get to see some of it, but I highly recommend doing a helicopter tour that can give you better views and it's quicker than having to do a ton of driving. Driving is nice as well as you can go at your own pace, but not sure how patient my kids will be.

Anyways...there's a ton more - but feel free to boardmail me with any other questions...we love the island and it's home for us - plus my wife is a travel agent if you need help booking anything- we'll be looking at a nailing down some fun things in the next few weeks.