Imagine a ship as being a floating town, almost every job on land exists on a ship designed to spend days at sea. I'll break down some of the jobs that would have to be performed on a ship at sea for you though.

Barber - Hair needs cutting, can't have it in your face or so long it gets caught in rigging or interferes with work.

Cook/Butcher/Baker - They would have livestock on board, chickens for eggs, goats/pigs for meat. All of that would need to be butchered/cooked. He would also bake bread, usually this would be a task performed at night so it would be ready in the morning, the Night Baker.

Jack of the Dust/Quartermaster - The guy in charge of storage, whether food or goods, the dust comes from the amount of flour he would move around and look dusty constantly.

Janitorial Duties - Everything from clean floors/tables to throwing trash/waste off the ship.

Helm/Steersman - Drives the ship

First Mate - Captain's enforcer type, makes sure what the captain wants done gets done. ie when Captain yells Loose all sails or some such, the First Mate knows who is supposed to be doing that and makes sure they do.

Master at Arms - In charge of the weapons/security of the ship.

Powder Monkey - Someone has to run powder and shot back and forth for the cannons after all.

Cabin Boys - Helps around the ship, usually with senior members of the crew, is young and is often used to help clean and as a powder monkey.

Navigator - Makes sure the ship knows where it's going and where it's been

Look Out - The guy in the Crow's Nest, keeping an eye out for other ships and sailing hazards.

Sailors - The rank and file did more than just man guns, they would be expected to know how to rig sails, patch sails, maintian weapons and gear, help repair damage to the ship, emergency repairs to the ship etc. Most would also be trained to help and actively help with other jobs such as cooking, storage, lookout, cleaning etc. Some could play instruments, and there would be tons of stories and things to keep men occupied in downtime as well.

Hope this helps you get an idea of what ship life is like.