I can't speak to the medieval period, but I can tell you a bit about the ancients. In Ancient Athens, soldiers were responsible for providing their own gear. The level of gear you could provide was partly responsible for determining your social status. The very wealthy could provide their own horses, and they made up the cavalry. The hoplites formed a sort of middle class, providing swords, shields, and armor and acting as foot soldiers. The lower classes, who couldn't provide anything, rowed on the trireme ships. The expansion of the Athenian navy and increased reliance on those ships actually helped drive Athens toward a democracy, since it put the rowers in a position of power.

The situation was similar in Republican Rome, with the wealthy equestrian class providing their own horses, and the foot soldiers providing their own swords, shields, and armor. War was also seasonal; these people were farmers, and they needed to tend their crops for some of the year. As the Roman territory expanded and their military needs grew, they moved away from this model and began recruiting from the lower classes who couldn't afford to be soldiers before and created a standing army financed by taxes.

For most of the later medieval period knights and levies were expected to provide their own kits - in the Assize of Arms 1181 Henry II of England laid exactly what each member of the various social groups and classes was expected to provide when called up to arms.

Similarly in 1318 King Robert the Bruce of Scotland's parliament laid out what equipment people were expected to have, for example

each layman of the kingdom having £10 in goods should have for his body in defence of the kingdom a sufficient haqueton, a basinet, and mailed gloves with a lance and sword.

However a knight or man-at-arms (or a huscarl if you go further back) serving in the household of a king or wealthy lord might expect to have some of their equipment provided for them.