Q. I was wondering if you'd done any comparisons on carry-on luggage. I've been doing a fair amount of flying, and that'll probably only increase. I'm looking for some sort of data so that I can find one of those popular roller bags that would fit into every overhead compartment. It's not so much that I'm looking for a brand (although that would be appreciated) but what dimensions do I need to be on the lookout for.

A. In order to be safe, the only rolling suitcase size that will pretty much fit in any overhead bin is an 18-inch model. Although 21- and 22-inch models are technically allowed, they sometimes have trouble fitting. Some regional jets have very small overhead bins and even an 18-inch model might have trouble fitting if the overhead bins are full. TravelPro makes an 18-incher that retails for about $150, but there are many manufacturers who sell models for less. When buying a new suitcase, be sure to get your bonus frequent flyer miles by shopping through the airlines' shopping malls.  You can sometimes get up to 10 frequent flyer miles for each dollar spent through these sources.