They have a long and short tour of the volcano state park on the big Isle. We did the short mainly because we didn't want to feel rushed. The long is supposed to be a bit more strenuous, but on that one you are supposed to be able to get near the lava flows.
We did the Fern Grotto river cruise / Luau on the second stop at Hilo. Nothing too strenuous there, and some possible photo ops.
On Waikiki and Maui we did our own exploring via taxi, revisiting places we had been before. Relaxing days, great beaches. For casual beach/shopping days, no excursions are necessary there. You can get to many good beach spots, rent chairs, umbrellas, snorkel gear, etcetera.