June,
You do not have to take CDW but if you don't you will have to leave a massive deposit (usually $1500 or more) in case you damage the car. CDW covers you for any damage that happens to the car you are driving. Without it you are liable up to the full retail cost of the car should it be in an accident even if it's not your fault. Definitely worth having.
SLI - this should cover you for up to $1 million at least. If you injure someone and they sue then you could end up with an enormous bill. You don't have to take this and of course we all hope not to have an accident or worse hurt someone but its a bit like medical insurance really if you don't have it the consequences can be just awful. It should also cover you against under-insured motorists which is a big problem in the US.
The various taxes, fees etc you don't have any choice about so they have to be paid.
Personally we always take the Virgin Platinum package - if you want more than 1 driver it is actually better value than the fully inclusive package.
You also are in a position where you will be wizzed through both check-in and check-out of your car at the airport because you are fully prepaid. Not everyone would agree that it is worthwhile of course but still better to be fully covered in my opinion.
Angela