Yes practice for every eventuality and carrying an extra pony is an excellent idea, used unfortunately it seems only in the north atlantic wreck dives to depth, because if you dive often enough, you will see so many "could never possibly happen" stuff actually happen. And in the process of practicing, hopefully I become a better diver myself. And I realize, that if I am an "experienced" diver, others will be looking to me as a role model, just as I look to other more experienced divers as a role model. Most diver errors are usually something really very simple that the casual eye of an experienced diver would have caught early before it became a problem, and even from a purely selfish perspective, I would rather end a dive 10 min early rather than ruin my two tank dive or dive vacation because we lost a diver, literally or figuratively, over something I could have remedied just by being attentive. we try to end a dive with 500 to 700 psi at surface so OOA can be something as simple or as rigorous as a shore exit in heavy surf, or a little too deep a little too long, or the extra minute to find the anchor line, the camera dropped, untangling a line, the weird stuff that can happen in just the last few minutes of a dive. So practicing for OOA and other misadventures and carrying a pony for self rescue can make diving a lot more fun for all concerned.
Then there are lots of things a diver can do while not being exactly an "unpaid dive master" that are really no big deal. If there are a number of new divers on the boat, I try to be the first into the water, the DM maybe busy getting them ready, so I am there in the water just in case, nothing I ever say. If an OW candidate has to swim to the shore from the boat, why I think I will swim too, just in case, and its also fun, but nothing I ever say, and I watch other divers set up their gear no matter how experienced, maybe I learn something maybe they learn something and hopefully, some is also watching me, just in case, no big deal.