Question

.p in the European feudal system under manualism what is the most significant economic commodity

Answer 1

Fidalis or loyalty the whole system was built on it . if you mean material commodity than that depends where you mean.
england = wool
scotland = fish
holland =cloth
france = wine/cloth
germany = silver 

as exports and the above should be considered as region not national states ,
during this whole period the only monetary system was the english or sterling penny.