Like most of the others I always carry a spare mask on me when I dive. I also carry a traditional 2nd stage reg w/ a QD fitting on it. Reason being, unless I'm helping with OW classes, I usually dive a ffm, and if something should go wrong, I can switch to a conventional mask and reg and clip my ffm to a d-ring. The one time I didn't dive with a spare mask and reg was about two weeks ago. At the lake helping DM a class and was finishing up a dive. Gave the sign that we were making our safety stop and as soon as I did, my omni-swivel failed, free-flowing air and letting water into my ffm. The bolt that holds the two halves of the swivel together loosened up just enough to allow the o-ring to pop out of place. We were right at 15 ft and had only gone down to about 25 ft max depth and it lasted the whole dive (about 30 minutes in 50F water) up to that point. My choices were either stay at depth and try to keep breathing my ffm, which as now flooding and breathing very wet on top of spewing what air I had left (flowed about 600 psi in about 10 seconds), pull it off, disconnect it from the QD fitting, switch to my octo and essentially be blind, or surface and be done with the dive. I chose to surface, using the normal ascent rate of course. Last time I dive without a spare mask on me.