I live in Canada and where I live, we get our health care for free. About 3 years ago, I had a pulmonary embolism that nearly killed me. While I was covered health care wise for the doctors and hospital stay, I wasn't prepared for the medication I needed to treat me conditions and complications ($220/wk), nor was I prepared for the 8 months off before I could return to the consulting work I was doing before.
This time around, I have stuffed away 8 months of emergency funding. This is on top of the money I need for the start up I'm on now. Built in to my top off are decision points; do I continue or exit, and part of that decision is whether I can afford to risk dipping into that emergency fund to continue my work.
So besides health care, which I realize you have to pay for in the US, make sure you have adequate funding for everything else ... loss of income, income potential and all of the drug costs assuming your health care plan doesn't cover them.
I'd also consider long term disability insurance. You're assuming you'll recover from whatever afflicts you, but what if it doesn't; then what?