WHAT do Catholics have to do, to get to Heaven?
Q. "What must I do to be saved?"
A. Sit down and shaddup.
Be in line when they're handing the grace out?
It is "ordinary" that someone who is moved by the Spirit will seek to be baptized. But starting with those martyred before they get a chance to be baptized (Baptism of blood, so-called) to the person who gets hit by a train on the way to his baptism (Baptism of desire) there are LOTS of hedges.
We can imagine God 'saving' someone whose culture and edumication led him to think Baptism wasn't important. And it's that kind of thinking that, IMHO, leads us to the "plene esse" or "fullness" kind of language.
GOd does not need sacraments to save people. But we'd say He prefers them, and that to have access to them makes certain graces certainly available.
Here's a 'practice' and a comment that may give some of the flavor:
If someone already baptized validly wants to become a Catholic, part of the preparation will involve confession. However, if someone NOT baptized wants in, of course he's going to be Baptized, and Baptism conveys forgiveness of all sin. So no confession is required. That's the practice part.
But we "contemplate" someone who, by grace, has such a complete repentance both in the sense of having r"emorse, etc. for past sins and in the sense of turning whole-heartedly to God, that his sins would be forgiven without Baptism.
However if that person wanted to be Catholic he would still need to be Baptized. There are other graces, after all, and only God can assess an internal conversion well enough to know someone had been forgiven.
And, finally, a question I've gotten two answers for is whether baptism pays the "Temporal penalty of sin" the stuff that gets dealt with in purgation. as I say, I've heard it both ways.
But remember, the "temporal penalty" is not about restoring the right relationship with God. That's taken care of. It's about (a) Those aspects of me that still like some sins and tend towards them, AND fail to love the relevant virtues enough and (b) in SOME, hard for me to get, sense, something owed to justice.
The example is if you break my window. I can say, Hey, forget about it, it's okay. So we're good. But you still might need, for justice's sake, to pay for the replacement AND to understand and 'fix, to the extent it lies with you, the carelessness of impulsivity or whatever led to your breaking my window.
WE're okay in any event.
I hope that is clear if not persuasive. (I didn't mean to persuade, only to convey.)