First of all LDW is a must; if you crash the car, you are totally liable for repairing/replacing the car; the Loss Damage Waiver (LDW) (also known as Collision Damage Waiver (CDW) in some places) absolves you of this. You would be crazy not to go with it.
The Supplementary Liability Insurance (SLI) covers any injury/damage to 3rd parties (not covered by LDW); I would also take this out.
The Personal Accident Insurance covers death or injury to yourself or passengers but if you have a decent travel insurance (which you will need for the USA), this will be covered by that so it is not really necessary.
Now, some car hire companies do a prepaid rate which you pay ahead of the trip which includes LDW and SLI and is a much less expensive option; in fact the daily rate sometimes works out cheaper than the non-prepaid rates which you still have to add the extras on to.
Hertz do these prepaid rates and I am pretty sure Avis also do them. It is the way to go and gives you peace of mind. The difference is that you have to pay when booking and if you cancel, you will lose the cost of the first day's rental.