Not sure what kind of carryon you prefer (given you may carry your regulator or other life-critical equipment) or where you shop, but I find that locksmith shops and safe dealers usually offer a generous selection of locks (and prices), as well as experienced, specialist personnel who give good advice. Even relatively small towns usually have at least one locksmith.

Members of the that trade are expected to adhere to serious ethical standards. I trust real locksmith employees more than random help at big-box stores that carry locks and make keys, which isn't to say they're perfect.

For me it's also a plus that these stores are usually locally-owned, so what I spend there goes directly to providing a service I've liked and into the local economy, rather than an online giant who may harvest my personal info unless I pay cash.

If you use a standard frame-and-fabric wheelie, unethical screeners determined to get into it (or convince LEOs to find PC) will just use a blade; I see little point in using a lock that's more secure or costly than zipper pulls or the bag itself.

Combo locks are usually low quality, but eliminate the need to carry keys which may alarm a WTMD, get lost, or be confiscated. At Doane's in Manhattan, and Pep Boys on a rural highway, I've seen cheap combination locks that are so unusual (for example, an unlabeled four-way directional paddle instead of numbered wheels) they would probably baffle anyone without lock skills, and the solution stays safely in your brain.