I see this used way too often in the wrong context.

Preppers are preparing for the "martial" side of things. The home protection, the looting, the convoys, that kind of physical stuff. Preppers are preparing for either neighbor vs neighbor combat (to put it nicely) or "urban combat."

Survivalists are the older hippie generation trying to survive through whatever happens. Also, younger people fit into this category if they are tongue-in-cheek and only worried about surviving.