My basic configuration stays the same, with additions and subtractions according to environment. I try to take only what I think is needed, but I'm still growing and learning as I'm exposed to new environments. For example, I've got my tropical singles rig and warm-water cave rig configurations down fairly well, but having done only a handful of cold-water deeper dives, it might take me a wee while be fully comfortable with my kit. A session of five in the quarry ought to help before I hit the open water. As for a drysuit and the potential addition of an argon bottle, when I can afford them...well.
As I was saying, I try and keep the line-up of equipment, assembly and placement pretty uniform. I use the same mask and fins on all dives. I also use the same single-loop harness whether I'm diving singles or doubles. That way, the positioning of cutting tool, lights and so on always remains the same. I always use the same wrist slate and gauges, although I'll add a decompression computer to one of my forearms, set my recreational computer in gauge mode and leave off the compass on a cave dive. The SMB will also go by the wayside, but the spool stays dangling off my butt D-ring and is joined by a couple of spool/reel-friends. I use a can-light and two back-ups in the caves, but only one of my backups might come with me on a simple day-time warm-water reef bimble. Two back-ups only at night. If so, the back-ups will be clipped off on the same spots on my harness as they are in the caves. Obviously, I'll switch out wings if diving singles or doubles. I use a long-hose and bungeed back-up whether I'm diving singles or doubles, too.