On most modes of transportation you can take any size of banjo with you. A standard banjo in its case does not meet airline carry-on regulations, but most airlines let any musical instrument case into an overhead compartment if it will fit. Banjos usually fit*; many guitars don’t.
If your instrument won’t fit, or the carrier doesn’t allow it as a carry-on, you’ll need to check it. Regardless, you’ll need two pieces of luggage.
All of my capo-ble banjos, except the first, have a 22” string length, and are about 32” long. That means one will fit in a 36” suitcase. There are several brands of airline-acceptable suitcase that are as long as that, catering mainly to golfers. Mine, shown above, is a Pivotal. I made a cradle for the banjo, but, really, you can turn the bridge down and pad the banjo with clothes; it will do fine.
I find it a great convenience to pack everything in one case.
That’s an advantage of the capo-ble banjo, but not an exclusive one. There are several short 5-string banjos on the market. If you want one that will fit in a 36” suitcase, get its exact measurements before you buy. (A 36” banjo will not fit in a 36” suitcase; 36” is the outside dimension. My 32” banjo just fits.)
*Not much fits in the overhead compartments of small local planes.