we have all lost a sea pass at least once,adult and kids) as soon as you realize it just go to the pursers office and get a new one. We have never had anyone use the lost passes. they sell a clip chain to carry your sea pass around your neck, we have found that very helpfull.
Speaking of the seapass, I was surprised that they were not connected to an lanyard (SP?) or something to wear around your neck or attach to a belt loop. So, my suggestion is that if you can gain access to one of these things they will come in handy in keeping up with your card!!
I'm wishing that I was still onboard!! (Got off a week ago yesterday! LOL!)