Regarding a non-baptised person, the clear answer is no, you cannot receive any of the sacraments, such as confession and Holy Communion.
Regarding the room mate, who is baptised in a Protestant church, the answer is more complicated. From the 1993 DIRECTORY FOR THE APPLICATION OF
PRINCIPLES AND NORMS ON ECUMENISM (at
vatican.va/roman_curia/pontifical_councils/chrstuni/general-docs/rc_pc_chrstuni_doc_19930325_directory_en.html ):
"b) Sharing Sacramental Life with Christians of Other Churches and Ecclesial Communities
- A sacrament is an act of Christ and of the Church through the Spirit.130 Its celebration in a concrete community is the sign of the reality of its unity in faith, worship and community life. As well as being signs, sacraments—most specially the Eucharist—are sources of the unity of the Christian community and of spiritual life, and are means for building them up. Thus Eucharistic communion is inseparably linked to full ecclesial communion and its visible expression.
At the same time, the Catholic Church teaches that by baptism members of other Churches and ecclesial Communities are brought into a real, even if imperfect communion, with the Catholic Church 131 and that “baptism, which constitutes the sacramental bond of unity existing among all who through it are reborn… is wholly directed toward the acquiring of fullness of life in Christ”.132 The Eucharist is, for the baptized, a spiritual food which enables them to overcome sin and to live the very life of Christ, to be incorporated more profoundly in Him and share more intensely in the whole economy of the Mystery of Christ.
It is in the light of these two basic principles, which must always be taken into account together, that in general the Catholic Church permits access to its Eucharistic communion and to the sacraments of penance and anointing of the sick, only to those who share its oneness in faith, worship and ecclesial life.133 For the same reasons, it also recognizes that in certain circumstances, by way of exception, and under certain conditions, access to these sacraments may be permitted, or even commended, for Christians of other Churches and ecclesial Communities.134
- In case of danger of death, Catholic ministers may administer these sacraments when the conditions given below (n. 131) are present. In other cases, it is strongly recommended that the diocesan Bishop, taking into account any norms which may have been established for this matter by the Episcopal Conference or by the Synods of Eastern Catholic Churches, establish general norms for judging situations of grave and pressing need and for verifying the conditions mentioned below (n. 131).135 In accord with Canon Law,136 these general norms are to be established only after consultation with at least the local competent authority of the other interested Church or ecclesial Community. Catholic ministers will judge individual cases and administer these sacraments only in accord with these established norms, where they exist. Otherwise they will judge according to the norms of this Directory.
- The conditions under which a Catholic minister may administer the sacraments of the Eucharist, of penance and of the anointing of the sick to a baptized person who may be found in the circumstances given above (n. 130) are that the person be unable to have recourse for the sacrament desired to a minister of his or her own Church or ecclesial Community, ask for the sacrament of his or her own initiative, manifest Catholic faith in this sacrament and be properly disposed.137"
