Since it is for a test side I would go for two bowlers and one batsman. If one was allowed four choices, I would have taken on the second batsman and that would have been ideal. The reasons are the following
1. All minnows are going to perform at a level lower than their opponents, thats a given considering their stage of development but those who have shown themselves to be not so terribly out of place have, mostly been those with better bowling.
2. Batting as a cricketing skill develops faster and first in underdeveloped countries because of the inherent glamour attached to the wielders of the willow and because most kids love to hit the ball with a stick than a stick with a ball. Thus the minnows will invariably come with a level of batting skills that makes them look at least moderately skillful in batting conditions. To reach the next level they need to be faced with tougher conditions and better bowlers than they are used to.
3. Following from 2 above, the better bowlers will help to upgrade tha bating skills of the side the reverse is unlikely to happen.
4. If there was one or more of them who, while fitting the batsman's or bowler's role was also an all rounder of sorts, it would make a great choice for obvious reasons
Thus I would go with the two best bowlers in the world and they have to be selected for their wicket taking abilities for they are in the side to get the opposition out and not to contain them. The solitary batsman on the other hand, has a different role to play. Being alone he needs to play the sheet anchor around whom the rest would bat. Thus I would prefer him to be solid of technique, have an ability to play long innings (bat through the innings if possible) and not be bereft of stroke play for the score board must move along. His first job, however, is to try and make sure the team is not routed and next to see if a total can be reached that would give the bowlers a fighting chance to push for a win.
Ideally the batsman would be an opening batsman but there is no Jack Hobbs or even a Gavaskar around today so I would settle for the next best - the number three so that the fall of wickets can be stemmed as early as possible.
The selection of bowlers as far as variety is concerned would be a bit difficult. Ideally the two main bowlers should be able to bowl in tandem for maximum effect thus a pair of quicks suggests itself but then we need to try and cover all conditions. I would like to take a high strike rate quick and a spinner with the same quality, both with lot of lateral movement. For the quicker bowler, it would be great if he moved it in the air too. Unfortunately thats not a very common trait as of date.
The two bowlers would do a lot of bowling between the two of them thus consistency and ability to bowl at the highest level for prolonged periods (with both old and new ball for the quicker bowler) is a very important criteria.
If one had to pick from history, then a Barnes or a Richard Hadlee for the quicker bowlers role and for the batsman there is the obvious choice of Bradman, Hobbs if one wants an opener and Sobers for batting at number three (he could and would have batted there but for non-cricketing reasons) and provide an invaluable third bowler. For the spinner, even from history, I would pick Murali :-)
If eligible as of today (having retired from Tests), I would pick Murali as the spinner, if not I would pick Swann.
If eligible again, I would pick McGrath as the quick bowler, if not then Steyn although he may not be able to bowl the longer spells that a two horse attack may need from him.
For batsman, I would not look beyond Dravid and Ponting with Dravid getting the nod for his better technique against both spin and pace, his ability to counter the lateral movement off both types of bowlers and for his temperament. I think he scores over Ponting in this and the team with just one world class batsman needs someone with his all round batting skills which are marginally better than Ponting - (throughout the length of their careers mind you).
I am leaving out Sachin for he has shown no inclination to bat at even number three although that is where the best batsman in the side should, ideally, bat. Dravid on the other hand has opened, inspite of his mental block against it, and shown that only his preference for number three stopped him from filling this spot when India needed it so desperately.