I use a wing system, but I do have a couple of accessory pockets that I use when I am diving wet... I take one off and use my drysuit pockets when I am diving dry.
I carry the following:
1. A DAN Safety tube with a 100 foot finger spool, the kit also includes a storm whistle, mirror and glow tube (came that way).
2. An inexpensive spare mask in one drysuit pocket pre-adjusted to fit.
3. A backup BRIGHT LED flashlight
4. A line cutter (always, always, always)
5. An air powered horn on my power inflator hose when in the ocean.
6. Wet notes
7. When diving in the quarry where people are training, I carry a rescue pocket mask. When diving in the ocean, I don't.
8. My backup Dive computer when on a longer multi-dive day dive trip where I need to pay attention to residual nitrogen... otherwise not.