Cash or card

I'm going to O'ahu for 5 days and wondering how much cash to bring? I'm coming from the UK so need to convert some before I go. My friend and I are assuming that all the little snack stands, food trucks, markets etc. Will be mainly cash? I have a credit card I can use too but I'd rather not due to fees. Any ideas on how much cash I should take? Was thinking £100 a day