What knife should I take if traveling

One of the most important things is a full tang. The tang is an extension of the metal of the blade into the handle. In knives with a full tang, it goes all the way through the handle. This improves stability, control, and durability. Cheaper knives with partial tangs will have the handle break off over time.

In a chef's knife, you want a blade from 8 to 10 inches long, whichever is more comfortable.

You can also either get a forged or stamped blade. I suggest reading this article on the differences. To summarize, forged blades are softer, easier to sharpen, heavier, and have a bolster. Stamped blades are sharper, harder to sharpen, lighter, and have a welded on a bolster if any. With current manufacturing processes forged is not necessarily better than stamped. You should make your own decisions. All crap knives are stamped, but not all stamped knives are crap.

This brings me to one of the most important points: It must feel good in your hand. Don't buy an expensive knife just because it's expensive, or you recognize the name. Go to a store that will let you use the knife, Williams-Sonoma will do this. If you can, bring a carrot in your pocket and actually cut that in the store.

_{I'll do some research on steel quality and update this later.}

A really well-sharpened santoku-style chef's knife is usually my choice. But, it does depend on the type of slicing... such as thick/thin discs, wedges, or dicing.

While I understand that a serrated blade can help with slicing a super-ripe tomato, when I want really thin disc-shaped slices, something very sharp and preferably a thinner spine. The favorite in my kitchen is definitely a Henckel santoku chef blade. Some versions can have a very thick spine, and wouldn't work as well, though. This type of choice is also more utilitarian if you're cutting any other veggies at the same time, or making additional cuts in the tomatoes, such as when you're also going to be halving the discs or full-on dicing.

Things I like the thinnest slices on are a ham and cheese melt, roast beef sammy, a sub for the road, and sometimes for a garnish. (hors d'œuvre, anyone?)

Also, when I'm cutting tomatoes into wedges, I also like to use this same type of sharp, non-serrated blade. Otherwise, I find it harder than necessary to do the smaller divisions after the 1/4-of-a-tomato size. I nearly always do 1/8 or 1/12 sized wedges for salad, so it isn't terribly often I use a "real" tomato knife. When I do, is when it's for a lunch and I don't want to sully a larger blade, or when doing large batches. Getting the core out is certainly easiest with a smaller, serrated blade.