Traveling by air today requires planning and learning not to assume anything.  But that hasn’t stopped people from believing that they can still rock up the airport just in the nick of time to catch their flight.  Understanding these misconceptions will help avoid nasty surprises:

1. If your flight is cancelled, you'll get a free hotel and food.  

This amenity has generally gone the way of free bags, and it says so in the fine print of airline contracts of carriage (found on carrier websites). That said, looks can be deceiving: When one of my employees' flights was cancelled this summer, she was surprised to see the beleaguered gate agent handing out hotel vouchers good for a 'special room rate'. On a hunch, she called the hotel and asked, how much for a room? She was quoted the same price as the voucher.

 2. Security won't be too bad.

The day after Southwest's October computer glitch delayed hundreds of flights, a friend was scheduled to fly Southwest out of Salt Lake City. She knew the glitch had been fixed but decided to get to the airport a little early "just in case". Unfortunately, hundreds of others had the same idea and security lines were massive. "There was no way I was going to make my flight," said my friend but then a TSA agent glanced at her boarding pass and told her she'd been randomly selected for PreCheck; she then zipped through security. Why take a chance on random selection when you can join PreCheck for only $85 for five years? You may not run into a computer glitch but you will find crowds during the holidays.

3. Non-refundable tickets always include some exceptions.

Not with some airlines. Sure, there is an occasional exception like the time Spirit refunded the non-refundable ticket of a dying man, but this happened only after social media exploded in outrage (the dying man had been a veteran) and most of us have no idea how to trend-on-Twitter. If you have a very good reason to cancel a ticket, go ahead and ask (nicely) but prepare for disappointment. Non-refundable tickets are called non-refundable for a reason.

4. Size and weight limits are for checked-bags only.

More and more airlines post baggage police at the boarding gate to eyeball carry-ons, and if these stern folks say a bag is too big, they will take it away from you for checking. Look up the airline's baggage policies before you pack and stay within the limits. If your bag is taken away, grab any valuables and other important items such as eyeglasses, medicine or electronics and stash them on your person.

5. There's always room for a carry-on.

Not so. My friend on the Southwest flight in #2 said there was no bin space on that plane; she had to cram her carry-on under the seat where her feet would normally go. Fortunately, it was a squashy bag but it ate up most of her legroom and left her exasperated "Southwest might as well charge for bags like everyone else," she said, "since everyone seems to use carry-ons!" Don't listen to her, Southwest.

Rick Seaney is an airline travel expert and the co-founder of FareCompare.com, an airfare comparison shopping site