"All salvation comes from Christ the Head through the Church which is his Body" CCC 846.
CCC 836 "All men are called to this catholic unity of the People of God.... and to it, in different ways, belong or are ordered: the Catholic faithful, others who believe in Christ, and finally all mankind, called by God's grace to salvation."
Being fully Catholic is not by itself enough. "Even though incorporated into the Church, one who does not however persevere in charity is not saved." CCC 837.
What abaut the ancient affirmation "Outside the Church there is no Salvation"?
The so-called "damnatory clauses" which appeared in the Athanasian Creed, and other ancient liturature, only apply in today's understanding to those who "knowing that the Catholic Church was founded as necessary by God through Christ, would refuse either to enter it or to remain in it."CCC 846. However, the Catechism of the Catholic church says at section 847 that: "...Those who, through no fault of their own, do not know the Gospel of Christ or his Church, but who nevertheless seek God with a sincere heart, and, moved by grace, try in their actions to do his will as they know it through the dictates of their conscience - those too may achieve eternal salvation." See the section called "Outside the Church there is no Salvation."
This marks a refinement in church teaching from previous times. For example, the catholic encyclopedia of 1913's article on Church says: St. Ignatius of Antioch writes: "Be not deceived, my brethren. If any man followeth one that maketh schism, he doth not inherit the kingdom of God. If any one walketh in strange doctrine, he hath no fellowship with the Passion" (ad Philad., n. 3). Origen says: "Let no man deceive himself. Outside this house, i. e. outside the Church, none is saved" (Hom. in Jos., iii, n. 5 in P. G., XII, 841). St. Cyprian speaks to the same effect: "He cannot have God for his father, who has not the Church for his mother" (De Unit., c. vi).
St. Thomas Aquinas in responding to the question of whether receiving the Eucharist is necessary to salvation answeres in part: "the reality of the sacrament is the unity of the mystical body, without which there can be no salvation; for there is no entering into salvation outside the Church, just as in the time of the deluge there was none outside the Ark, which denotes the Church, according to 1 Pt. 3:20-21. And it has been said above, that before receiving a sacrament, the reality of the sacrament can be had through the very desire of receiving the sacrament. Accordingly, before actual reception of this sacrament, a man can obtain salvation through the desire of receiving it, just as he can before Baptism through the desire of Baptism..."
However, be sure to read Nostra Aetate, a document of the Second Vatican Council on the Church's relations with those of non-Christian religions.
Speaking of the Orthodox Churches, in the recent document Dominus Jesus the vatican said: "The Churches which, while not existing in perfect communion with the Catholic Church, remain united to her by means of the closest bonds, that is, by apostolic succession and a valid Eucharist, are true particular Churches. Therefore, the Church of Christ is present and operative also in these Churches, even though they lack full communion with the Catholic Church..."
In speaking of ther Protestant communities, it says: "not Churches in the proper sense; however, those who are baptized in these communities are, by Baptism, incorporated in Christ and thus are in a certain communion, albeit imperfect, with the Church. Baptism in fact tends per se toward the full development of life in Christ, through the integral profession of faith, the Eucharist, and full communion in the Church.
"The Christian faithful are therefore not permitted to imagine that the Church of Christ is nothing more than a collection - divided, yet in some way one - of Churches and ecclesial communities; nor are they free to hold that today the Church of Christ nowhere really exists, and must be considered only as a goal which all Churches and ecclesial communities must strive to reach". In fact, "the elements of this already-given Church exist, joined together in their fullness in the Catholic Church and, without this fullness, in the other communities". "Therefore, these separated Churches and communities as such, though we believe they suffer from defects, have by no means been deprived of significance and importance in the mystery of salvation. For the spirit of Christ has not refrained from using them as means of salvation which derive their efficacy from the very fullness of grace and truth entrusted to the Catholic Church".