Most of them are but personal accident isn't (you are covered by your travel insurance). Anything relating to damage/loss to the car or liability to third parties is vital.
Contact insurance4carhire.com for cover that almost always outdoes anything offered by the hire companies. You will of course need insurance, but the hire companies'cover is very expensive.
KARL is right. I advised some friends of mine to take up car hire excess insurance from a British company and they were overjoyed to find that it saved them an absolute fortune when they hired their car in the States. The face of the car hirer fell considerably when they told him that their excess was covered by their own insurance. It's definitely worth doing.
Just to clarify: The cover by insurance4carhire is a full replacement of the car hire company's policy - in the US you separately buy full insurance when hiring a car (not just excess cover) because there people can usually refer to their own car insurance policy for cover of any hired car in addition to their own car (at home). You save a lot by providing your own insurance this way.