My 1994 J30 w/ 212k miles started and ran fine this morning. Came out of coffee shop - dead. Was able to jump start the car, but its dies immediately upon removal of the jumper cable. Advice?

It sounds like your alternator is not charging.

here's a quick way to tell if its your alternator, if you manage to get the car running on its own electricity, remove a battery cable, doesn't matter which one, just yank on off, if it runs, your alternator is good, if it dies, and I mean like immediately dies, then your alternator is bad, and the way it sounds to me, your alternator is shot.