What is the basic item for much of medieval trade?

Answer 1

depends on where you traded
in Europe it was things for everyday use like wool, timber, food etc...
in Africa/ Arabia it was salt, gold and copper, of course also food and slaves
things from Arabia, Africa, Asia and Israel etc (gold, silks etc) were of course brought to Europe by the merchants but so expensive for the normal people that only the nobility or wealthy people could buy them.

Answer 2

wool