British Airways may present the one-bag traveler’s stiffest challenge. Flyers departing from the UK or transferring through the UK are limited to one carryon with NO personal item - at least in coach class. The rules are a little unclear. BA did drop its infamous 6kg/13 lb. limit for carryons in 2006, but the BA site does show 6 and 7kg limits for some of its franchise airlines. And I’ve seen some info that implies the one-bag rule is only for coach and some that suggests it is for all passengers. The one-bag restriction does not apply (for the moment) to US-originating flights; you still get one carryon plus the personal item. Still this rule may hit you if you fly to the UK on a US airline, spend some time thare, then fly on BA to a non-US destination. Beware and check with BA first.
Woe to the onebagger if BA’s rules represent a worldwide trend. Loss of the personal item would put extra stress on the one bag packer.