I have learnt tons from the onebaggers over the years, but my concern with the onebagging concept is that "one bag" is not the same thing as "travelling light". My aim is to achieve the latter, rather than the former for its own sake.

Two small bags, in general, make far more sense to me. This way I get better weight distribution, more convenient access to essentials during the flight/journey and a day bag that doesn't make me look too obviously like a tourist at the other end.

I appy a 7kg rule for my primary bag because (a) that is the most I feel comfortable carrying on my shoulder and (b) that is the carry on limit for most of the airlines I fly (eg QF, CX). So, not too dissimilar to Till's 14lb rule of thumb... However, I don't weigh my handbag and neither has any airline so far!. That probably adds about 2-3kg to my total load on most trips (typically includes all my tech).

Lots of onebaggers seem to adopt the approach of packing a smaller bag inside the primary bag, which I find is rarely practical for me, because the second bag, if it is suitable for use as a day bag, tends to take up a disproportionate amount of space inside the primary bag. Personally, I am not prepared to sacrifice that additional space when it is more convenient for me to carry the second bag separately anyway!

From a business perspective I always found onebagging virtually impossible, but I guess that depends on what work materials you need to carry and what level of professional attire is appropriate in your field.