Where in the Bible does it tell you that, annalex? The bible says to believe and be baptized. Belief is the main point and baptism comes as obedience but if a person believes on his or her death bed, and isn't baptized, does that person go to hell? I think not. There isn't anywhere I know of where the eucharist is really necessary. What is necessary is putting your faith and trust in Jesus Christ. But, you've been over all this before, I'm sure.
Necessity of Baptism:
3 ... Amen, amen I say to thee, unless a man be born again, he cannot see the kingdom of God. 4 Nicodemus saith to him: How can a man be born when he is old? can he enter a second time into his mother's womb, and be born again? 5 Jesus answered: Amen, amen I say to thee, unless a man be born [again (*)] of water and the Holy Ghost, he cannot enter into the kingdom of God.(John 3)
37 ... What shall we do, men and brethren? 38 But Peter said to them: Do penance, and be baptized every one of you in the name of Jesus Christ, for the remission of your sins: and you shall receive the gift of the Holy Ghost.
(Acts 2)
Necessity of Eucharist
54 ... Amen, amen I say unto you: Except you eat the flesh of the Son of man, and drink his blood, you shall not have life in you. 55 He that eateth my flesh, and drinketh my blood, hath everlasting life: and I will raise him up in the last day.(John 6)