1) Gilgamesh flood - so, this agrees with the bible in large part. Sounds like the Babylonians and the ancient Hebrews might have lived in the same region...and suffered the same flood.
2) Easter - um, what's this got to do with "ancient myths". Do you mean, adopting the name of a pagan goddess for the celebration of the resurrection of Christ, which was based on the centuries-old Jewish Passover, not on a Germanic goddess who was probably not even worshiped at the time of Jesus? Which ancient myth are you claiming to be related to the Christian celebration of Easter?
3) Isis - I assume you are trying to relate to Mary. Let's compare
Isis - funerary assistant to dead king / pharaoh; protects dead against evil
Mary - dead, doesn't do funerals
Isis - 4 sons
Mary - only one definitely; others possibly
Isis - considered to be the wife of Horus, the Pharaoh god
Mary - considered to be the wife of Joseph, a guy
Isis - married her brother, Joe Bob Osiris
Mary - not into the cousin-lovin'
Isis - later, becomes mother of Horus instead of his wife, and since Osiris was dead, they had to resurrect him so he could do the nasty with his sister and make Horus
Mary - didn't have any of these issues
Isis - has to leave with her son to escape her jealous brother Set, who had already killed her husband / brother
Mary - has to leave with her son and husband to escape the frightened King Herod - so far, the nearest similarity, and it's not very close at all
Isis - heals her son of a poisonous scorpion bite
Mary - nope
Isis - tricks sun god into giving her his secret name so that she has the magic to raise her brother from the dead so that she can do the nasty with him
Mary - uhhhh, I don't think so.
Isis virgin birth - well, she
a) turned herself into a kite by magic and then
b) flew over Osiris' dead body to become pregnant
Mary - no, didn't have to do any avian necrophilia to get pregnant
4) Saturnalia - "Saturnalia is the feast with which the Romans commemorated the dedication of the temple of the god Saturn,"
Christmas - "the celebration of Jesus' birth"
not very similar...
5) Mithras - 1st century Roman religion - wonder where they got those ideas????
Well, the flood is obviously not plagiarized, but simply an account of a similar flood or, possibly, even the same flood.
Easter - we have biblical texts pre-dating our earliest knowledge of the Germanic Eostre by at least 5 centuries.
Isis - about as similar as Hulk Hogan and Richard Simmons. No, I take that back - those two are much more similar than Isis and Mary.
Saturnalia - well, most are well aware that Christmas is celebrated on the day that was formerly Saturnalia. There certainly seems to be no similarity with the biblical account of Jesus' birth and Saturnalia, though.
Mithras - no need to retroplagiarize when you are the one being plagiarized...
Jim, http://www.jimpettis.com/bibles/