I have both Keen and Teva sandals which have good support and can handle being soaked. If you don't have those regular sneakers will be fine, just be prepared to have to dry them out.

Have a wonderful time!

Ditto the Tevas, sneakers are a second choice for me, mostly because I hate getting sand in my shoes, and with the sandals, I can just unstrap them and brush my feet off. But you'll definitely want a sturdy sole - those volcanic rocks can be brutal!

If you're willing to go 'off-trail' a little, you'll get the longest walk if you start at the playground at Warwick Long Bay - get off the bus there, walk through the playground and go all-terrain down the hill to the beach. You won't be the first, there are little footpaths here and there, it's just not an established trail. Then you just head to the right and keep on going! My favorite days involved hiking the trails, swim gear under my shorts, towel in my daypack and having a nice swim at the end of the trail before heading home.
(Remember you can't ride the bus in wet shorts or swim gear.)

And if you have room for one of those little trial-size bottles of baby powder, shake a little bit on your feet and the excess sand will fall off, so you can put your socks and shoes back on!

I knew you both would have the answer. Didn't know that about baby powder. You are fantastic! Thank you!!