My go-to bag is still a Gator; it fits a number of ultra-portables and has room still for some paper. I'm not sure that I'd want to travel with a typewriter that was any larger or heavier as it would be too cumbersome, and besides, an ultra-portable easily fits under an airline seat, something I don't think larger portables would be able to do.

A "true" portable is really any model smaller than a standard; it would be tempting to claim that a portable is any typewriter that has its own travel case, but there were a few standards with protective cases and that would probably confuse matters.

Years ago I started calling the really small (flat) portable models, ultra-portables. My reason for this was simple: the definition of practical portability has changed dramatically over the years, and in a world of ever-shrinking airplane seats and invasive security protocols, I felt it was important to distinguish between machines that were easy to move between the thrift store and your home, and those that you could actually travel with. Sure it's still possible to lug around a large and heavy portable, it's no great effort if you're using a car (I traveled with a standard once), but it's a surefire way of turning simple trips using other modes of transportation into arduous journeys. 

I own about half a dozen different models that are named Junior, but they don't include the Royal. If you're talking about the model from '30s, my bigger concern than being able to carry it around would be its durability when subjected to the rigors of travel. As a rule I only use 'newer' machines, those from the '50s and '60s, those that I wouldn't shed a tear over if they were to be damaged or lost. Although I've never scientifically proven it, I feel typewriters from those two decades are more robust and can handle travel in a bag far better. I use an Olympia Traveller most often, and it seems to shrug off being handled like any other piece of carry on luggage. 

Uwe wrote:

A "true" portable is really any model smaller than a standard; it would be tempting to claim that a portable is any typewriter that has its own travel case, but there were a few standards with protective cases and that would probably confuse matters.

Years ago I started calling the really small (flat) portable models, ultra-portables. My reason for this was simple: the definition of practical portability has changed dramatically over the years, and in a world of ever-shrinking airplane seats and invasive security protocols, I felt it was important to distinguish between machines that were easy to move between the thrift store and your home, and those that you could actually travel with. Sure it's still possible to lug around a large and heavy portable, it's no great effort if you're using a car (I traveled with a standard once), but it's a surefire way of turning simple trips using other modes of transportation into arduous journeys. 

I own about half a dozen different models that are named Junior, but they don't include the Royal. If you're talking about the model from '30s, my bigger concern than being able to carry it around would be its durability when subjected to the rigors of travel. As a rule I only use 'newer' machines, those from the '50s and '60s, those that I wouldn't shed a tear over if they were to be damaged or lost. Although I've never scientifically proven it, I feel typewriters from those two decades are more robust and can handle travel in a bag far better. I use an Olympia Traveller most often, and it seems to shrug off being handled like any other piece of carry on luggage. 

From this, I would say the portability of a typewriter is relative--depending upon the circumstances involved with getting it from point A to point B.  It could be argued that a standard Royal HH upright manual is more portable than a Royal RE of the same vintage because the HH is self-contained, whereas the RE relies on an outside power source.  But could it be said that a Royal HH, being self-contained be more portable than, say, a Smith-Corona Coronet Super 12--which is not as self-contained and relies on a power source?  While both are heavier than blue blazes, the Coronet Super 12 is of a smaller size, and therefore, logically more portable than the HH, even though it's not self-contained. 

Just this ol' cowpoke's opinion:  a true portable typewriter, I think, would be self-contained (though not always necessarily a manual, as I've seen 6-volt Smith-Coronas and a myriad of battery-powered electronics), light enough to reasonably manage, and, as was said, can stand up to the rigors of whatever mode of travel is put before it.
 

Yale wrote:

What kinds of typewriters are small enough to fit in a laptop sleeve?

If you have a largish laptop sleeve, try a Canon Typestar or a Rooy portable.