Thanks for the comments. I've taken dozens of flights through Africa and the Middle East with this camera bag, which is basically the size of a "backpack" that a college or high school student would use to carry a load of textbooks. However, it will carry about $10,000 in camera bodies and lenses as well as a small laptop. Since it is much smaller than a carryon suitcase, it escapes notice. It fits under the seat.

I wouldn't mind paying a reasonable fee for the extra weight, but I'm concerned that there is no apparent mechanism for doing so.

A separate issue is that I travel with a CPAP (medical device) and battery. US and European carriers have no issue and have never counted this against my cabin baggage allowance. SA has the same policy, but its ground staff in Africa don't understand this. I've had repeated issues followed by repeated apologies, but nothing ever changes. This is one reason I'm taking Ethiopian.