A belt around your belly during night is one of the old school penances for reminding one not to eat out of pleasure, but only out of need.
Acts of penance are acts against ones earthly pleasures. We are taught by Christ to hate all pleasure that lead to sin. Therefore we are called to make acts of reparation for the sins, that are committed by penance.
Fasting is the oldest and most known form of penance. Prayer can also be penance in case you don’t like prayer. Prayer goes against pride and is therefore the most efficient instrument for becoming humble. Once in this state of humility, the next step is penance.
May this not only be on my lips, but also in my heart.
Hail Mary, full of grace, the Lord is with thee, blessed art thou among women and blessed is the fruit of thy womb Jesus. Holy Mary, Mother of God, pray for us sinners, now and at the hour of our death. Amen
(I make the sign of the cross)