I have a 25 or so foot 50 amp cord (hard wired to the coach on one end), plus I carry a 25 ft 30 amp cord, plus a 25 ft heavy gauge 20 amp cord, plus adapters (mainly for power tools, such as my electric impact wrench in case I need to change a tire). So far if I have a 50 amp site, the 50 amp cord has been long enough, though I have seen some creative 30 amp situations, such as 2 or more RV's sharing a single power post, or power posts at public electric only campgrounds being mounted behind a back in space.
If I am in a 30 amp site I generally use the 25 ft 30 amp cord, and connect it to the 50 amp cord, as the 30 amp is a lot lighter weight and less hassle. (I am aware of the potential voltage drop)