Baptism and Eucharist are the principal ones. Baptism is the initiation ritual which gave the right to participate fully in the other rituals, particularly the eucharist.
Baptism is in use early in the church.
Romans 6.1-11, dying with Christ and being incorporated into his body. Being liberated from the requirements of the Mosaic law. Mk 1 and parallels refers to the baptism of Jesus himself. Mk 10.38 refers to the death of Jesus as a kind of baptism. Matthew 28.19, the Trinitarian formula for invocation.