Minecraft wiki entry for Building_a_cruise_ship, associated text: Concrete (good building block, could be used outside the ship)
Wool (useful inside the ship, but be careful using it near fire or lava, as it is flammable)
Planks (can be used inside the ship, but it is also flammable, so make sure that fire cannot spread to it)
Carpets (decoration block, also usable inside the ship, but again, it is flammable)
Torches or glowstone (useful for lighting)
Glass pane or glass (can be used as windows)