My approach is similar to Alpheus' with a few caveats:
For PRS/NRL matches:
I have the Armageddon Gear armband that Kudu referenced above. The plastic cards that come with it are a bit bigger than a business card and have velcro on the back. They also come with a fine point wet erase pen and an "eraser" pen. Generally I just use it on my wrist and write: target identifier, range, dope and low/high wind value for each stage. If I feel there's a benefit to a particular stage of not having to break cheek weld and have info right in front of, I'll make a 2nd pared down card that goes on the sidewinder that will have: target identifier, either holdovers or dope (depending on strategy for said stage) and whatever my starting wind call for each target is.
For team/field matches (with ranging on the clock) or if it's pouring rain:
I use a Sunrise Tactical wrist coach and a grease pencil. It's a bigger surface to write on which works better with the "coarse" writing you get with a grease pencil and a grease pencil still works fine in the rain, unlike the wet erase pens. Mine has a flap that opens so place for more info inside. I put a blank sheet of paper on which I've drawn a 1/2 circle broken down into 3 quadrants in the outside facing flap so I can quickly draw target locations and ranges/dope as I find them. The inside flap has another blank sheet where I can write additional info down and I also have plasticized cards with a mil-ranging chart and hard copy of my dope. At the end of the stage, I use my glove/finger to wipe the flap clean.