In a medium bowl, toss the pineapple with the sugar and rum. Spoon 1/4 tablespoon of the butter in the center of each sheet of foil and top with the pineapple. Sprinkle with the caramels. Bring 2 sides of the foil up over the fruit and fold to form a seam across the top. Fold the remaining 2 sides to seal the hobo packs completely.