What does it take to be "saved"?

Yesterday, our cell group met at our house for the last time before we move. We handled chapter 29 of the Screwtape letters, where Screwtape exhorts Wormwood to look after his patient's physical well-being as far as possible, since his untimely death will result in a failure for the Lowerarchy. Lewis points out that time is the devil's greatest ally in drawing people away from God. This led our discussion to consider the statement that people make that "I am saved", as if it is a once-off thing. We considered if that is really how it works, and if so, what are the requirements to "be saved". Does one just have to believe in Jesus? Do you have to change your life? Do you have to repent? Confess your sins? How about baptism? Is that necessary? Or just an optional extra? If you can "lose" your salvation, when do you lose it, and (how) can you get it back? Well, these are thorny issues, so of course we didn't get down to an actual solution. But the discussion was interesting, especially seeing how different people in the group reacted/responded to the question and discussion.