To try to simplify, keep in mind that it is recommended to bring at least:
CDW (Collision Damage Waiver), also called LDW (Loss Damage Waiver), depending on the rental company. This is an excess exemption that must be at least equal to the value of the car you are renting. Some credit cards (such as Visa Premier) cover CDW, so check with your bank for details about the excess exemption (but be aware that Visa Premier does not cover CDW for 2- and 3-wheelers, 4x4s, and vehicles of a certain standard, such as Bentleys, Cadillacs, Chevrolet Corvettes, etc.).
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LIS (Liability Insurance Supplement), also called SLI or ALI, depending on the car rental company. This is a civil liability insurance for all material or bodily damage caused to third parties (pedestrians, other drivers, etc.). LIS usually covers up to $1 million! The legal minimum is $50,000, except in California, where the law does not impose any imposition on car rental companies! So, check the value! Other insurance may be offered instead of LIS: EP (Extended Protection), often offered to foreign tourists.
Other insurances may be offered, such as PAI (Personal Accident Insurance), which covers you (driver and passengers) in the event of an accident, including ambulance expenses, hospital, etc. However, the PAI limits of car rental companies are usually very low and, in any case, you are already theoretically covered by the multi-risk insurance you have taken out for your trip or by the insurance of your bank card (Visa Premier or Gold Mastercard) with which you have paid for your trip.
Many rental companies also offer roadside assistance (“Roadside Assistance Protection” at Alamo, “Premium Roadside Assistance” at Hertz, etc.), which covers flat tires, lost keys, lack of fuel, etc. This assistance quickly becomes very expensive on a three-week trip (about $5 per day), without really being useful unless you don’t know how to change a tire or are particularly forgetful.