Course you could just use the vuescan app and no need any additional equipment other than whatever scanner you have now.
Can't quite fit my existing scanner (part of an all-in-one printer) into my briefcase.
Cn you bring the document home? Or, is there a networked scanner where you tend to go? Not trying to be silly but...seriously, how often are you out and about where you really need to scan something "right now" that can't simply be brought with you back to home base?