Answer by Stephanie Vardavas,
Pull out your cellphone as soon as it becomes clear that your flight is significantly delayed, even if it is not yet officially canceled. Call your airline and ask them to re-book you. And don't forget to nail down your seat assignment while you have them on the phone. They will not charge you a change fee and by calling in quickly you will have a better chance of getting on a desirable alternate flight. Flights are so crowded these days that relatively few aisle and window seats will be available, so be sure to confirm your seat assignment if you can. This is the #1 most important thing you can do, and it has worked for me countless times. Just a few weeks ago, I was flying IAD-DEN-PDX and my first segment out of Dulles was delayed for mechanical issues. I had a first class upgrade and was comfortably settled, so I was reluctant to give up that seat but I was at risk of missing my connection and I absolutely had to be in Portland the next day. I called United and they booked me into the last available first class seat on the nonstop from Dulles to Portland, which was scheduled to depart an hour later but would still arrive in Portland before my original flight did (and which I had not originally booked because it would have added $150 to my fare). I gathered up my belongings and hauled ass down to the other gate, boarded my nonstop, and had a lovely ride back to Portland. They serve hot fudge sundaes in first class on that nonstop!
If the flight is canceled due to weather or air traffic control issues, the airline by law does not owe you a hotel room, a meal voucher, or any other accommodation. If the flight is canceled due to the airline's own equipment troubles, then the airline does owe you accommodations, depending upon the nature and duration of the delay. If the airline is responsible for a delay of a few hours, you'll get a meal voucher. If the airline is responsible for an overnight delay they will give you a hotel voucher and tell you where you are staying. By now, if you followed my first piece of advice, you already know when you are scheduled to fly out in the morning. When you get to the hotel, there will be a large number of delayed passengers all trying to check in at the same time. Try to sit near the front of the hotel shuttle bus for that reason, to get off the bus and up to the front desk faster. While you are checking in, ask if you need a reservation to catch the hotel shuttle back to the airport for your morning flight. If you do, book it right then and there, or you run the risk of not being able to take the shuttle when you need to. You can also ask if you are eligible to earn points in your hotel loyalty program. Sometimes, you will be. Have your membership numbers stored in your phone so you can handle this quickly without fomenting a lynch mob among the passengers waiting in line behind you.
By way of prevention, I always avoid connections through Chicago in the late fall / winter / early spring if I can. I can't tell you how many nights I have spent at the O'Hare Hilton or other ORD area hotels, even though such stays have never been part of my travel plans. If you are delayed at O'Hare and there is bad weather that you think will ground you overnight (snow, lightning, etc.), call the O'Hare Hilton first thing and ask about availability for that night. The Hilton is connected to the main terminal by underground tunnel, so you can get there without having to brave the elements. On a really bad night, they will sell out completely and then you will have to stay at another hotel, which will require you to go out into the weather and catch a shuttle bus that may or may not arrive soon.
Keep your sense of humor and perspective. You will need both. With very few exceptions, a delayed trip is not ultimately a really big deal, even if it seems to be of huge importance in the moment. It's not your fault, and no one will hold it against you. For your sanity's sake, try to take the inconvenience in stride.
If you have only carry-on bags, you will be in a better situation, but I check bags all the time and it is not a big deal. In my carry-on, I do have clean pajamas, a change of clothes plus an extra t-shirt or two, maybe some extra socks and underwear, and the basic toiletries I need to get through an overnight stay (basically, my TSA clear plastic baggie of liquids and gels, plus a stick deodorant and toothbrush), in addition to laptop and other essential electronics like power/charging cables for laptop, phone, iPad, Kindle, etc., and any medication I may need. I'm a lawyer, so if I have a handwritten document or handwritten notes on a printed document that are irreplaceable, those go into the carry-on too. Do not count on having access to your checked bag during a delay or after a cancellation, but most airlines, especially the legacy carriers, will give you an amenity kit. Just go to the airline's baggage service office (typically on the perimeter of the baggage claim area), tell them you are delayed overnight, and ask politely. The amenity kit is a little nylon bag of goodies normally given to business or first class passengers on intercontinental routes and may contain some or all of the following: a tiny toothpaste tube, toothbrush, lip balm, sleep mask, mints, foam earplugs, maybe a little tube of skin lotion.
The airline will reroute your checked bag to your destination (or wherever you ask them to) as best it can, and will deliver the bag to you at no charge (although you may wait a day or two or even longer, depending upon how bad the delay is). I got stuck in the big snowstorm in Amsterdam a couple of years ago, a week before Christmas. I was too slow to book into a Schiphol airport hotel and ended up spending almost five hours traveling back to central Amsterdam via train (normally a half-hour trip) to stay in my downtown hotel for one more night, then having to return to AMS in the morning (by taxi) for a rescheduled flight. This was all made easier by the fact that by this point I had with me only a messenger bag and a 22" wheelie bag, inside which were the various clothes and necessaries I mentioned above. I did not see my checked baggage till it was delivered to my parents' home in Baltimore five days later, on Christmas Eve, just in time for me to unpack and wrap the various little gifts I'd picked up during my ten days in Europe. (Hang onto your little baggage receipt until the bag shows up.)
When you are returning the next day for your rebooked flight, if you can print out your boarding pass at your hotel, or carry it in your phone, DO THAT -- you can avoid massive queues at the airport by doing so.
And last but by no means least, be nice to all the reservationists, gate agents, and flight attendants. They have the ability to help you, and they are only human. If you are nice to them they will go out of their way to help you. In any event, the problem is not their fault, and it's terribly inappropriate to take out your frustration on them.