Forgetting to read the fine print. Not packing a change of clothes. Confusing a.m. and p.m.

In a previous column, I asked you to tell me about your worst travel mistakes. Did you ever!

Most are not errors of commission as much as they are errors of omission: leaving something out, for example, or forgetting to verify a reservation.

I've also made my share of travel mistakes. Of course, it's not so much the error that matters — it's what we learn from it. That's why you're reading this.

Here are some of my favorite mistakes:

1. Assume nothing. Chris Sandberg got a notice that his United Airlines miles were about to expire, but was told he could preserve the miles by earning points by staying at a Starwood hotel. "After my stay, I was credited with points in the Starwood program, but not with United," he says. Why? Turns out Starwood could only "convert" blocks of 1,000 points at a time. The hotel was happy to sell him another 200 points so that he could rescue his miles. If he'd made arrangements with United beforehand, that might have been avoided. Now Sandberg always finds out the details before making a reservation.

2. The Mexican car insurance surprise. Car insurance in Mexico is a requirement, and the cost is added to the agreed-upon rate.

Haven't heard of this? Neither had Kimberly Williams when she rented a car in Cancun through Travelocity recently. "We got the cheapest policy, but it cost an extra 15 bucks a day for a compact car," she says. On out-of-country rentals, no matter what your travel agent tells you, always check with the car rental company to find out if there are any additional requirements.

3. Check out the need for a car. Sara Rueben thought she needed to rent a car when she visited Sydney, Australia. She thought wrong. "We stayed at the Wyndham, which is pretty much in the heart of the city," she remembers. "Then we got to the resort and realized that not only did we not need it because the public transportation was more than adequate, but there was also a $30 per night fee to park." Next time she visits a big city, she vows to call the hotel or resort ahead of time to find out if she needs a vehicle.

4. You say Chuck — I say Charbel. When Chuck Andary booked a ticket from Detroit to Los Angeles, he never considered that his legal name — Charbel — might render his ticket useless. Then he learned about the Transportation Security Administration's new Secure Flight rules, which require that the name on your ID match your ticket.

He called his online travel agent, Expedia, for advice. It couldn't change the name on his ticket, and the airline wouldn't either. Luckily, he was able to board because the TSA is still phasing in Secure Flight.

5. Morning or night? Cyndi Russell booked a flight for her son to attend summer camp, but she misread the "p" as an "a."

"The week of the flight, I received a "time to check-in" e-mail, and I was horrified to see that I had purchased a ticket for 8:40 p.m. instead of 8:40 a.m.," she says. Her airline wanted $500 to fix the mistake — a change fee, plus the full fare ticket.

6. Check for additional fees. Extra fees are the lifeblood of car rental companies, airlines, hotels and cruise lines. "I got socked with a $13-a-day fee from Hertz for a recent rental for adding my spouse as an additional driver," Britt Skrivanek says. "The rental agent told me there was no fee for spouses. After returning the car three days, later I got a bill with the fee on it."

7. Expect delays, and pack accordingly. Maryann Portone made this rookie mistake when she started flying: "To avoid carrying a lot on to the plane, I put all of my clothes and sundries into my checked luggage," she says. But when her luggage was delayed for 24 hours, she had to buy shampoo, toothpaste and other necessities. "I had to sleep in my clothes for one night and couldn't go to the pool or the beach until the third day of my five-day vacation," she says. Now she always packs a pair of underwear and travel-size sundries in her carry-on bag.

Christopher Elliott is the ombudsman for National Geographic Traveler magazine. You can read more travel tips on his blog, elliott.org, or e-mail him at celliott@ngs.org.