A TFN Swiftsure class destroyer is larger than the largest wet navy warship of the 20th century, yet it only has a crew of 36. Enormous hydrogen tanks fill much of the interior of the ship, while weapons systems, sensors, shield projectors, and the like pierce the hull. Less than 20% of the ship is used by the crew. The rest is patrolled by various robots linked to the bridge and engineering's mainframes. Most of the ship remains in a vacuum, with no life support whatsoever.
The largest climate-controlled, pressurized chamber is the biosphere. All ships, warships or civilian, keep at least one garden of genetically engineered plants and micro-organisms for oxygen, food, waste processing, etc. Biospheres are usually the only places aboard ship to receive direct sunlight, albeit filtered to protect from deadly radiation. Spacers use these areas for relaxation and meditation.
The gardens provide food, albeit a vegetarian diet. The main staple for the spacer is the proto-carb "cube," a slice of processed soy protein, and vegetable matter. It has no flavor, it's texture is slimy to leathery, and it stinks. Fortunately, when mixed with real food, vegetables from the biospheres for example, it takes on the taste and aroma. Whenever possible, though, spacers will take liberty on planet, to eat the local cuisine, no matter how bad its reputation.
In spite of the necessities of wartime, and the harsh demands of the military, crew members aboard ship end up with a lot of down time. Most will use this time to exercise in the small gyms, play computer games, socialize, or write letters home. For many others, these activities get redundant, so they try to expand their minds. They will most often study astrophysics, computer programming, astrogation, and military strategy. Anything that may challenge their minds and further their careers. Art also inspires. Many of the most universally renowned paintings, carvings, symphonies, and novels, have come from bored spacers.
source: Terran & Avarian Fleet Book