It's a club rule that every diver must carry a surface marker buoy (SMB). Either you inflate it and take it one the dive, or you carry a delayed SMB (dSMB).
Even if it weren't a rule, I would always take at least one, and usually two, SMBs. They're too important and useful to risk being without one on a dive.
My main dSMB is an A.P. Valves dSMBi - a self-inflating dSMB. It has a small aluminium cylinder attached to it, charged from the main cylinder before a dive, which makes it amazingly easy to launch. No unclipping of direct feeds, no purging of regulators, no dumping air from the BC, no trying to catch exhaled air. Just open the bottle a little and watch it go.
Unlike some self-inflating dSMBs, this one is basically a normal dSMB with a bottle added. This means that, if for some reason the bottle can't be used, it can still be filled the normal way.
I used duck tape to put my name on the side - dSMB's all look the same, I like my surface cover to know which one is mine.
The only downside is, it's a lot bulkier than a standard dSMB.
I also carry a standard dSMB with me, folded (not rolled) in a pocket. This will only be used if I let go of my main dSMB.
