Do most of the grocery stores accept debit cards and/or credit cards?
The grocery stores and most merchants accept either debit or credit cards. However, a few of the dining places do not, The Pizza Cafe and Kualapuu Cook House for example.
It’s a good idea, when visiting Hawaii, to bring travelers checks and a little cash. As a caveat, most merchants on Molokai do not change currencies, so be sure to have US denominations with you.