There's a surprising amount of modern Christian lore that actually comes from The Divine Comedy, the granddaddy of all ascended fanfic.

Transubstantiation is kind of in the Bible. Matthew 26:26-28

While they were eating, Jesus took bread, and when he had given thanks, he broke it and gave it to his disciples, saying, “Take and eat; this is my body.”

Then he took a cup, and when he had given thanks, he gave it to them, saying, “Drink from it, all of you. This is my blood of the[a] covenant, which is poured out for many for the forgiveness of sins.

The discussion of transubstantiation is just how literal "my body/blood" is.

That humans eventually become angels.

Though, there was one human who did, in an apocryphal book. And then was elevated yet again to being a second diety; there were apparently strains of Christianity which were DUOtheistic! https://en.wikipedia.org/wiki/Enoch

This is much more of a list of stuff commonly believed by Catholics, not so much by Christianity as a whole.

Purgatory aswell

https://www.britannica.com/topic/purgatory-Roman-Catholicism

So is "God helps those who help themselves"

The Trinity is clearly taught in the Bible. Sure, not in explicit Athanasius creed form, but Jesus even said "Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit" (Matthew 28:19).

Notice how "Name" is singular, implying the Father, Son and Holy Spirit is one thing, or at least equal. Jesus is referred to as God, the Father, and the Holy Spirit are also. And it's made clear that there is one God. The Athanasius Creed is just the Trinity clearly defined in a single text. Clarifying interpretation (like the Nicene Creed).

Seven deadly sins are based off of various sins listed in the Bible, but most of it has kind of been overhyped and overemphasized. It's useful for giving a rough idea of what sin is, but it's been meddled with over time.

I wonder if enough technicians go to heaven could the pearly gates can be automated so St Peter can finally retire.

It comes from Matthew 16

15 “But what about you?” Jesus asked. “Who do you say I am?”

16 Simon Peter answered, “You are the Messiah, the Son of the living God.”

17 Jesus replied, “Blessed are you, Simon son of Jonah, for this was not revealed to you by flesh and blood, but by my Father in heaven. 18 And I tell you that you are Peter, and on this rock I will build my church, and the gates of Hades will not overcome it. 19 I will give you the keys of the kingdom of heaven; whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.”

[end quote]

So, yes, authority given to St Peter to "bind and loose" in heaven and on earth. How that's supposed to work alongside it being Jesus separating the sheep from the goats is anyone's guess.

The reason this takes place at the "pearly gates" is because the new Jerusalem descending from heaven in Revelation is described as having giant pearls for gates.

He just checks the no fly list.

Neither of these mention St Peter at the pearly gates, though. The biggest addition the Apocrypha makes is a record of someone praying for the dead. Protestants generally still do recognise the Apocrypha, but just as historical records and not authoritative, hence not a part of the Bible.

Although some would argue there's a lot of foreshadowing.

Can't speak for Catholics but most reformed protestants (evangelicals) will be being taught their sins are already washed away and any judgement for the 'saved' after death is only about their quality of walk with god and quality of reward in heaven, it's not a heaven/hell judgment. That's only for the 'unsaved'.

Many Christians cremate.