If you were to be marooned indefinitely on a desert island with one person who holds a PhD in any subject, who would you choose? Your companion can be from any era; we will assume that he or she is in the prime of life. Honorary degrees do not count (so unfortunately you cannot bring Dr. Seuss).
Good question. Everyone I know who has a PhD is a well-rounded person who’s enthusiastic about many things outside his or her own field, so I could hardly lose no matter which subject I chose.
More likely than not, there are people out there with PhDs in absolutely fascinating subjects that I would never think of. More’s the pity.
I’ll have to go with something like Comparative World Literature of the Middle Ages, but I may change my answer later when I read other people’s answers.
I’m tempted to be practical and go with Engineering - but then there’s no guarantee that an Engineering PhD would be practical!
Oh, wait - is the OP asking for a particular person who happens to hold a PhD? In which case I initially misinterpreted the question. I’d have to go with my friend James, who has a PhD in Genetics - we could maybe make some interesting new life-forms, or failing that play Scrabble together and compose cryptic crosswords for each other to solve :).
It wouldn’t matter to me what the field the PhD was from as long as s/he gave good head.
My husband, in about 5 years.
If it can’t be someone I know, then it would possibly be Stephen J. Levitt, the economist. I know nothing about economics but his brain is fun and works completely differently than mine, so I imagine together our problem solving skills would be complimentary.
Yes, I meant a specific person. I’ve been considering Buzz Aldrin or perhaps Jared Diamond.
Can’t you at least get a DFA in that these days?
Oliver Sachs? What good stories he has.
I don’t know if he actually has a PhD or not, but I would take “The Professor” from Gilligan’s Island. He can make useful stuff out of just about anything. 
I think someone with a PhD in Engineering would be the most practical if you were wanting to get off the island, but I could see where a MD or a Biologist could be useful too.
My college roommate, who has a PhD in biochemistry. I already know we get along well together. It’d be great fun for about the first week until the boredom sets in and we’re both sick of coconut.
And in the general sense, with the exception of my old roommate, I’d not pick someone with a chemistry PhD. Most of them that I know are the opposite of the well-rounded interesting persons that Gala Matrix Fire knows. Or maybe I’m just tired of my coworkers.
Dr Feynmann
Carl Sagan or Stephen Jay Gould.
But only because Danica McKellar doesn’t have a Maths PhD yet.
Hmm… Do you choose for survival traits, skills and knowledge? Or just for good companionship? If I wanted to ensure I’d get off the island, I’d choose my sister. Within about a month one or the other of us would have built, from scratch, a suitable ocean-going vessel to get away from the other. 
I wonder, did Graf Zeppelin have any degrees?
If we’re being allowed fictional companions, I’d choose Cyrus Smith, from Jules Verne’s The Mysterious Island.
Or, failing that, Captian Nemo…
I would pick someone with a JD so we could spend our time gathering evidence to eventually sue the party who caused us to be marooned in the first place. Does being marooned toll the statute of limitation?
My father. His degree is in chemical engineering, but he has also built boats, circumnavigated the world, and designed and built his last two houses.
And yet, he cannot patch a two foot diameter hole in the hull of a wooden boat or built an outrigger canoe out of the salvage. Once you get on the island with the Professor, you never get off, at least not permanently. It’s like being sent to The Village.
Just one “n”. Aside from being dead, Dick Feynman had something of a reputation in private for being fairly cantankerous (and also a bit of a letch, which was apparently not an uncommon attitude in the CalTech physics department of the era). On the other hand, he was good at math, reasonably practical with his hands, a pretty decent portrait artist, and played the bongos expertly. You could do worse, I suppose.
Stranger
Whichever one has the most meat on 'em.
WVmom’s Dad.
Laughing Lagomorph, who knows many, many PhDs, almost all of whom are sadly NOT particularly well-rounded or knowledgeable/enthusiastic about things outside their chosen fields.
Since I have one, do I get to pick who goes on the island with me? Females only, and send pictures of yourself in a bikini so I can complete the scientific evaluation process.
Actually, as far as desert islands go, my Boy Scout experience would be far more useful than anything I learned in grad school.