Liability insurance covers your mistakes that cause damage to other cars or property.
Collision insurance covers damage to your own vehicle when it's your own fault.
Comprehensive covers theft, vandalism, fire, flood, animals, glass damage from debris, etc.—things beyond your control. Usually comprehensive is cheap.
Uninsured motorists' coverage covers damage to your vehicle caused by other drivers without insurance.
If you really want to cut one, cut collision. Then be prepared to pay the full cost of a replacement vehicle if your car gets totaled and it's your fault. Don't cut comprehensive.
As the OP mentions, if you have a car loan, then the lender requires you to have full insurance including at least the first three above, if not all four. You don't have a choice.