Interesting prepper question

A volcano in Iceland is spewing an ash plume all over Europe.  This is, of course, disrupting that most modern form of travel, aviation.  Having volcanic ash, which is really a microscopic shard of rock, sucked into your engine will really ruin your day.  Of course, you'll get a few seconds of glider time to add to your flight log, but it's unplanned.

The powers that be in Europe have prudently shut down their air travel network for the most part.  Thousands are stranded at airports and are scrambling for alternate means of transportation.  In Europe, that usually means the train.  Rail travel in Europe works very well, and to be honest is probably not much slower than flying once you take into account the amount of time it takes to go through security at an airport.

But what do you do if you're stranded at an airport in the US, where long-distance travel is usually either done by car or plane?  Amtrak isn't really an alternative. 

Let's say you're flying from Los Angeles to New York, with a layover in Denver.  That's probably the longest journey you will make in the continental United States.  You get to Denver, and a blizzard and ice storm comes in, stopping all air travel for the foreseeable future in Denver and the surrounding states. 

You aren't in LA, where you could just go home.  You're not in New York, where hopefully you'd have some people to assist you, either in business or personal life.  You're stranded in the middle of the continent with no real way of going forward or back. 

Best case scenario is you have friends or family in the Denver area who can take you in until you can get your travel mess straightened out.

If you're lucky and have the cash, you get to the rental car counter before the rest of the Golden Horde and get yourself a go-go mobile to get you back to LA.

If you can't do that, then if you have the money and you at least have some luck, you get into a motel to ride out the storm until transportation can be found.

But let's look at worst case scenario.  No friends or family.  The rental car counters are all closed because they're out of cars.  The hotels are all full to the brim. 

So you're stuck in the airport for the foreseeable future.  You have with you the clothes on your back, unless you can convince someone to get your bags out of the checked luggage area.  You may have some food and drink with you if you thought to bring some for the trip.  You may have some cash or a credit card to buy food at the airport, but that can run out fast.  Everyone and their brother who's stuck in the same predicament is at this very moment rushing through the food court and convenience stores to get what they can.  Maybe you have a book, or a laptop, or an iPod to keep you from going insane.  Hopefully, you packed a toothbrush and the small pack of toiletries the TSA will let you take on-board.  Did you put your necessary medication in your check baggage?

Can you go for 3 or 4 days on what you have in your carry on? 

Here's what I always pack in my carry-on no matter what when I travel by air:

1. Blanket - either a small thermal blanket or one of those space blankets
2. Water - After I get through security, I always buy two of the biggest bottles of water available.  TSA doesn't allow bottles of liquid through their checkpoints, so I'm forced to grin and bear it on the price of water.
3. Food - I always pack some snacky smores for munching, but I also pack two or three energy bars for emergencies.  You can stretch this out for a day or two.
4. Communications - Always have a cell phone with you, even if you have to buy one of those disposable pay-as-you-go phones at Best Buy.   If you've got a laptop and can get access to a power outlet, you can use wireless Internet connections to stay in contact with home.
5. Entertainment - You'll always find two or three books in my carry-on.  A book of puzzles like crosswords and a pencil or two will give your mind something to do.  My iPhone is with me, of course, but I always make sure I have the 110 to USB adaptor for it too, along with a charging cable.  If you've got a laptop, you can get absorbed in a video game to wile away the hours.
6. Toiletries - At the very least, I have my toothbrush, a small tube of toothpaste, and some baby wipes. You'd be surprised how good it feels to brush your teeth and wash your face.  Even if you can't get a shower or shave, little things like that can make you feel human again.
7. Medication - I always hand carry my meds.  In addition to my normal daily medication, I make sure I take along some extra Benadryl, Immodium, and Pepto-Bismol in case I get sick during a trip.  Nothing worse than trying to find a drug store when you've got a raging case of Montezuma's Revenge.

As for what you do when you're stranded, I suggest finding a place where you can see all around you to camp out.  Hopefully the airport has TV monitors so at least you can see CNN or whatever they're piping in.  Don't go off somewhere quiet to try to get some sleep.  Being alone makes you an easier target, no matter if you're a 6'4" lumberjack or a 4'10" housewife.  Stay with the crowd, and try to group up with people you can spend extended time with.

And until you find a way to either continue your journey or go home, try to keep a good attitude.  Every jerk in the airport is going to be harassing the staff either for information on when they can get out or for help in getting the things they need but didn't think to bring along.  Being polite to those around you, especially airport staff, will go a long way to keeping everyone from turning into wolves.