It is always recommended to be covered by travel insurance if you are going on vacation. In the event that you are unable to travel due to unforeseen circumstances, such as ill health or severe weather conditions, then some compensation can be sought.  Contact your insurance broker for details on travel insurance or one of the many travel insurance companies that operate online.

Travel both domestic (within the USA) or to foreign lands can benefit from travel (or trip) insurance.  You never know when you may need to cancel your carefully planned vacation.  See an article in the South Florida Sun Sentinel called Travel insurance can rescue a vacation gone awry 

The SFGate has an article on travel inurance about TravelSafe's trip cancellation insurance which has an "any reason" cancellation option.  New policies cover anytrip cancellation

You should look for your travel insurance at the same time as you are booking your vacation.  Some insurers offer extra benefits when the insurance is booked within 10 days of placing your initial deposit.  It also shows good faith in the event that you need to make a claim.  Always keep a paper trail of receipts and invoices - it all helps in the unlikely event that you need to claim on the insurance.

If you are traveling to the USA from overseas it is also vitally important to have adequate health insurance - healthcare costs within the United States are high.  Even a small wound could end up costing you hundreds of dollars in medical bills.