Skin: Commonly described as fair, clear or white. (ref: Diodorus,
Hair: Long hair was the fashion, described as “thick and shaggy like a horse’s mane”, even satyr-like due to the treatment with limewater; the aristocracy favored large moustaches; and the Celts generally shaved their entire bodies, Caesar’s account further proven by iron razors and sprung iron shears found at the site of La Tene. Hair was variously mentioned as blond, flaxen or tawny, but either way further lightened artificially with lime. (ref: Caesar)
Height: Frequently described as very tall - taller than the Romans, the women bigger and stronger than Roman women. (ref: Diodorus, Marcus Borealis)
Fitness: The Celts are frequently attributed by historians with great physical prowess (“with rippling muscles”). In fact, fitness was so inherent to their customs, that any man exceeding the standard size was punished. (ref: Strabo)
Food/Diet: Grains, fruits, nuts, meat. Caesar describes them as living on “milk and meat”; Poseidonius also points out bread and fish. Cattle, dogs, hares, fowl and geese they grew only for entertainment or practical use.
Fashion: Striking clothing, dyed and embroidered in bright colors, striped or checkered cloaks. They wore form-fitting pants called “bracae”, tunics that were red, purple or multicolored, elaborate torcs as symbols of power, brooches, bracelets, hairpins and rings. They took great interest in their appearance, so that not even the poorest wore soiled or ragged clothing. Even cosmetic grinders have been found in Iron Age British contexts, signalling they might have used eyeshadow or blush. (ref: Diodorus, Flavius Arianus, Propertius, Amnianus Marcellinus)
Tattoos: The Britons were unique for their tattoos and the blue woad they painted their bodies with. (ref: Caesar)
Music: The most famous Celtic instrument is the Carnyx, styled in the form of an open-mouthed boar, emitting harsh, discordant sounds suited for battle. (ref: Diodorus)
Personality: High-spirited, hospitable, fond of feasting, straightforward, frank, courageous, etc. (ref: Diodorus)
Notable traditions: The head as the throne of the soul, hence the custom of severed heads as trophies; comradeship was important (those with most followers considered most powerful). (ref: Polybius)
Traveling: Some tribes were nomadic, ridden with wanderlust, others settled down in farming communities.
Sexuality: Homosexuality was common and they were very nonchalant about it, showing they were comfortable with varying sexual orientations as well as sexuality in general. (ref: Athenaeus)
Spirituality: Animism (the notion that everything is animated with life, including nature), the worship of nature, a vast pantheon of gods that differed from tribe to tribe, but had common deities as well (ie. Cernunnos).