I think any Act of Contrition would be acceptable, but this is probably the most commonly used in Trad parishes.
"O my God, I am heartily sorry for having offended Thee, and I detest all my sins because I dread the loss of Heaven and the pains of hell, but most of all because they offend Thee, my God, who art all good and deserving of all my love. I firmly resolve with the help of Thy grace, to confess my sins, to do penance, and to amend my life. Amen."