It's pretty ironic how Gilligan, the skinniest castaway on the Island, represents Gluttony. Food was his motivation, thus he just never accomplished anything without getting something to eat in return. Gilligan just wanted to be rewarded for the various tasks and chores he took on. In order to get things done on the Island, Mr. Howell would tempt Gilligan with money, Ginger tempted Gilligan with lust (a few innocent kisses), the Skipper would threaten Gilligan with anger and punishment (like hitting him on the head with his hat), but it was Mary Ann's Coconut cream pies that turned him into a mindless slave drone. That was what got him to fetch for water, cut down trees, or help Mary Ann with the laundry.

(This closely parallels Scoobydoo and his desire for Scooby snacks)

Pie wasn't the only food that satisfied Gilligan's appetite; look at the other things he feasted on: radioactive spinach, "Mind Reading" sun flower seeds, Soap, all of the citrus fruits on the Island (episode: "V" for vitamins.) In almost every episode Gilligan is either eating a banana or fishing for dinner. Lets face it, Gilligan thinks with his stomach and not with his mind.

Just one of the seven reasons why they were never able to leave the Island.