[QUOTE=lottie;6742]I can understand why you would want a spare mask strap - but a spare mask? Would that be necessary or is that down to the ole scout motto of "Be prepared"??? [QUOTE]

I draw from my early mishaps
I was on a post-dinner night dive on my first Tubbataha liveaboard. Because the divemaster and I were seated beside each other on the chaseboat, we inadvertently switched masks in the scramble for gear in the dark. In the course of the night dive, he and I had our own puzzled thought balloons: his mask was tigher than usual and mine was looser (turns out his strap had the beginnings of a tear that he was fond of ).
On the surface, while waiting for the others to scramble up on the boat, he and I compared our tally of marine turtles and, with the moon out from behind the clouds now, noticed that we were wearing each other's masks! As he handed me my mask, he fumbled and it feeeell (our lights were too feeble by then).
Imagine my chagrin with 4 more multi-dive days to go! I ended up buying from the liveaboard's shop (I didn't want to tell the DM for how much ).
Now, I have two spare masks, hehe. You never really know.