They usually number about 30-40 persons, including men, women and children. Most of their number will be adults. Because of the difficulties of raising and carrying infants, primitive cultures will practice a cruel birth control, spacing children and even committing infanticide when necessary. Thus, a clan will be 7/8ths full-grown combatants with hit dice commensurate with their mass.
Clans of up to 100 are possible but as the number increases so does the likelihood of a large clan breaking apart into smaller clans. Clans will be led by chiefs, who will be related to most of the clan and will possess an extraordinary ability to find food when it seems impossible to find. Chiefs will also remember the routes that must be travelled from food source to food source. This skill is more important than physical prowess. A chief's power is defended by lesser clan members who fear starvation if the chief is killed or forced into exile.
While primitive, tech 5 clans are aware of the threat - and opportunity - posed by more advanced outsiders whom they meet. Clans will therefore be extraordinarily wary of strangers. Long before the party encounters the clan itself, it is highly probable that the clan will be aware of them through individuals who will have heard or sighted the party beforehand. Remember that the clan is very aware of the environment while the players will not. Unless the players know precisely where a clan is encamped, it is virtually impossible that the party will surprise them.
That said, clans will never ambush strangers. They will know that strangers may have tremendous advantages in equipment and numbers - meaning that the death of ten strangers could result in a magically led vendetta that will inevitably wipe the clan out. Therefore, clans will prefer to make their number known to the party and ultimately meet in a place where the clan has the terrain advantage (different humanoid races would have different definitions of 'advantage'). Clans would then prefer to talk rather than fight.
In most ways, clans will be among the most peaceful of all cultures because they understand that in any confrontation with superior forces, they're bound to lose. They would prefer to trade information and goods, making friends with strangers. This makes them vulnerable to evil strangers - but note that most tech 5 clans can live their entire lives and never see anyone except the members of another clan perhaps once every two or three years.
Because there is no formal training or education, levels occur only because they have had obtained experience through direct combat. No individual will be above level 1. Fighter is the only traditional class. The clan has a 40% chance of having a shaman (see below) who will be a 1st level fighter as well has having very limited magical powers.
The only proficiencies will be the club or the javelin (a headless spear that will be thrown and not used in hand-to-hand combat). Domesticated animals will not be part of the clan. Weapons must be fabricated by hand, from stone, flint or wood. Armor does not exist - not because it couldn't be imagined but because it would be impractical to carry during long migrations.
Drovers are clans that specialize in herding animals. Tribes are agglomerations of clans.