Wow bunnyfoo,
That's a terrific idea!
We never had to get replacements, but we had a close call once. So close, that we thought we'd have to go home!
And that time we did go into City Hall and ask if there was anything we could do about replacing the lost passes. Unfortunately, the answer was no, as we had purchased the park passes at home and didn't know the numbers. (it turned out my DS had the tickets in one of those leg pockets in his shorts and we didn't have to go home after all!)
So I will go copy those numbers now and bring them with me for some peace of mind. Thx!