People of Bible times did not use utensils such as forks and spoons to eat their meals (read Gen 18:7-8), They picked up the food with their hands. But some dishes such as stew or gravy had to be scooped up with a piece of bread. This is the method of eating to which Jesus referred in this verse.
In John’s Gospel, this bread used to pick up liquid food is call a “sop.” Jesus handed the bread to Judas, clearly identifying him as the betrayer (John 13:26).
MARK 14:20 – He [Jesus] answered. . . It is one of the twelves, that dippeth with me in the dish [dips bread into the bowl with me, NIV]