1257 The Lord himself affirms that Baptism is necessary for salvation…
1277 Baptism...is necessary for salvation, as is the Church herself...
183 Faith is necessary for salvation…
1129 The Church affirms that for believers the sacraments of the New Covenant are necessary for salvation…
980 …This sacrament of Penance is necessary for salvation…
846 ...the Council teaches that the Church, a pilgrim now on earth, is necessary for salvation...
1816 …Service of and witness to the faith are necessary for salvation…
1259 For catechumens who die before their Baptism, their explicit desire to receive it, together with repentance for their sins, and charity, assures them the salvation that they were not able to receive through the sacrament.
837 …Even though incorporated into the Church, one who does not however persevere in charity is not saved.
2036 The authority of the Magisterium extends also to the specific precepts of the natural law, because their observance, demanded by the Creator, is necessary for salvation…
2068 …so that all men may attain salvation through faith, Baptism and the observance of the Commandments.
Council of Trent:
CANON XXXII.-If any one saith, that the good works of one that is justified are in such manner the gifts of God, as that they are not also the good merits of him that is justified; or, that the said justified, by the good works which he performs through the grace of God and the merit of Jesus Christ, whose living member he is, does not truly merit increase of grace, eternal life, and the attainment of that eternal life,-if so be, however, that he depart in grace,-and also an increase of glory; let him be anathema.
CANON IV.-If any one saith, that the sacraments of the New Law are not necessary unto salvation, but superfluous; and that, without them, or without the desire thereof, men obtain of God, through faith alone, the grace of justification;-though all (the sacraments) are not ineed necessary for every individual; let him be anathema.
Catechism of St. Pius:
39 Q: What are the conditions necessary to obtain Heaven?
A: The conditions necessary to obtain Heaven are the grace of God, the practice of good works, and perseverance until death in His holy love.
Compendium of the CCC:
207. What is life everlasting?
Eternal life is that life which begins immediately after death. It will have no end. It will be preceded for each person by a particular judgment at the hands of Christ who is the Judge of the living and the dead. This particular judgement will be confirmed in the final judgment.
208. What is the particular judgment?
It is the judgment of immediate retribution which each one after death will receive from God in his immortal soul in accord with his faith and his works. This retribution consists in entrance into the happiness of heaven, immediately or after an appropriate purification, or entry into the eternal damnation of hell.
Q. 476. Is grace necessary to salvation?
A. Grace is necessary to salvation, because without grace we can do nothing to merit heaven.
Q. 477. Can we resist the grace of God?
A. We can, and unfortunately often do, resist the grace of God.
Q. 478. Is it a sin knowingly to resist the grace of God?
A. It is a sin, knowingly, to resist the grace of God, because we thereby insult Him and reject His gifts without which we cannot be saved.
Q. 479. Does God give His grace to every one?
A. God gives to everyone He creates sufficient grace to save his soul; and if persons do not save their souls, it is because they have not used the grace given.