Should I purchase rental car insurance? What protection does my credit card provide?

From a comprehensive article posted on credit-land.com (emphasis mine):

So, credit card coverage includes damage and theft, but it does not cover personal injury, liability, or property. It also does not cover any driver who is not authorized on the car. Only the people named on the car rental agreement are covered. Also, certain types of vehicles aren’t covered – usually trucks, campers, and other specialty cars won’t be covered. Comparing with our side-by-side review of U.S. Car rental services, the only two items covered by any credit card rental insurance are LDW and CDW – car theft and damage. Supplementary coverage, personal coverage and medical coverage are not included in standard credit card rental car insurance agreements. SLI, PAI, and PEC are not included.

Credit card car rental insurance is always considered secondary coverage – it covers you if you don’t have other car insurance or if you do not purchase insurance from the rental company. A very important thing to know is that with any credit card rental insurance, buying the coverage from the rental company will invalidate your credit card insurance coverage. You can’t get coverage from both sources at once. However, if your personal car insurance has a deductible, then your credit card will cover that amount. Keep in mind, although your rented vehicle is protected, you will need a separate insurance to cover possible liability damages you may cause to the other vehicle or property involved in the accident. As always, the best solution is to be careful while driving.

There's also a handy infographic on the site, not included here because it's about 4 miles tall.

Some roads in Hawaii are very narrow with a lot of rocks and other obstacles. Check https://duckduckgo.com/?q=hawaii+roads&iar=images&iax=1&ia=images If you have plans to visit such places you might want to consider extra coverage.