Neat question. We always work our way to the back of the ship, usually the small aft deck on 7, as it is leaving Port Canaveral and take a few pictures. It is typically deserted or quiet and we have a little family time. The photos of the family leaning against the rail with the wake and port behind you are keepers. Last time we had one of the RCL ships trailing us, and my daughter looked particularly beautiful.
Speaking of traditions, I like the door thing. We do a tradition that started decades ago as a way to waste the last couple of pictures on a roll of film. We take a picture of everyone's feet on the last day of vacation. Silly, I know, but we have 20 years of feet pictures...hiking boots, swim fins, ski boots, sandals, bare feet. 2 pair before kids, more feet with kids, even more feet with friends and family. Yes, we make everyone stand in a circle and squeeze their feet into a photo --- and, yes, we do get some odd looks. To each, his own...