Well you need to define the term 'peasant'. Is it anyone who isn't noble or clergy, anyone who farms or a very specific class of farmers? read more
Most medieval peasants started warfare with staffs or pole arms that were considerably cheaper than swords. If the peasant had an occupation that gave a weapon from their trade, such as a woodsman having an axe or a miner having a pick, they used these weapons. After their first battle however, they could glean whatever weapons they could gather. read more