Rental car insurance is very confusing in Costa Rica. If use your credit card coverage, they will often put a very large hold on your card ($5,000) as a security deposit. And keep in mind some credit cards void their coverage if you go off of paved roads, which tends to happen in Costa Rica at some point.
The only strictly required insurance is the liability, which covers damage to other vehicles, etc. The others are optional and cover damage to your vehicle, with a deductible paid by you. I personally usually get full coverage for the peace of mind. But it can boost the price significantly, sometimes the insurance costs almost as much as the rental.
When reserving a rental car online, they will often not include insurance in the price. So after making your online reservation, be sure to call and speak with someone about insurance options and the price.