One flight-booking mistake cost my family nearly $3,000 and a day of travel. Natalie Becerra

I'm a veteran traveler who has booked more long-haul flights than I can count. But earlier this year, I made a very expensive rookie mistake.

While planning a trip, I came across a deal I couldn't pass up: a $317 one-way flight on Icelandair to Ireland with a multi-day layover in Reykjavik. It was essentially a way to take a trip within a trip without paying extra airfare.

The catch? The flight departed from New York, not our home airport in Florida. I'd be in New York a few days early, but my family would need to fly up to meet me. Booking separate itineraries was far from ideal, but I figured a five-hour buffer would be enough.

It wasn't.

A storm in New York canceled my family's JetBlue flight from Florida, and their replacement flight then couldn't land and was diverted to Virginia.…