2 quick race day questions

Hey everyone, my first tri back in a while is on Sunday and I'm flying solo.

What does everyone do with their car keys? I don't think there's a secure bag drop so I'm thinking of hiding them in my second water bottle. Thoughts?

Secondly, I'm a bit confused about my new power meter and my new watch. If I calibrate the PM with the watch before the swim start will that still be valid by the time I finish not drowning and get back to the bike? I've never used a PM in a tri before, so I've no clue. It's only a sprint distance, and I haven't trained with power very much, so it's not essential, but I'd like the figures to be fairly representative afterwards.