The common case would be to select the whole column, with ctrl + spacebar.
You could also select the current data region with ctrl + shift + 8 (in
other words, control + asterisk), in which case multiple columns would be
made to fit their contents.

If you don't select anything, then the autofit command would set the column
width based on the contents of the current cell. That's probably not the
typical case, but at least it does something that makes sense. Ha ha.
-Paul