While the news has been thick and fast with airlines and cruise companies offering to waive change fees and other kinds of restrictions, savvy travelers need to live by two rules: Check and re-check with your particular carrier and its changing rules, and think carefully about whether to cancel at all.
The reason for the second caution is this: Most flights are being cancelled by airlines, up to nearly all international flights and a majority of domestic flights. If the airline cancels the flight, you can claim a refund rather than a voucher or credit for future flights. Airlines don't publicize that; they'd rather keep the cash and give you a future flight.
But, some travel writers are warning, don't wait too long for a cancellation, since airline phone and online service lines may be super-busy, and if the plane does fly, and takes off before you get through to cancel it, you may have lost your chance for either refund or credit.
If you do find the time has gotten tight and you're on hold forever, find the Twitter, Facebook or other social media contact for the airline's customer service, notify them that you are trying to change your flight and cannot get through on their phone lines. That will give you a paper trail in case of a dispute.
If you do decide to go the change routes, check very carefully with your carrier; some early versions of waivers were more restrictive or applied to fewer classes of tickets; even newer ones may require you to complete travel within a fixed period, usually one year from the original date. For people with plans to travel to weddings or other one-time events, that may not be very helpful.