I have 2
DGX 600 flashlights (they have an aluminum body and take an 18650 battery, similar to many other brands). I guess if they were more fragile, I would treat them like a reg or a computer, but they can take a fair amount of abuse.
When I fly, I stick them in one of
these regulator bags, along with 2 sets of regs and my computer. I really have to cram all that stuff in there, so I am not worried about it shifting around. I then place the whole reg bag into my carry-on backpack, along with stuff I will need at the airport (chargers, 1 layer of clothes, water bottle, sunscreen, passport, etc). I pack 2 masks and stick one in each of the fin pockets. The fins, backplate, wetsuit, booties, etc go into a checked
mesh duffle bag, along with most of my regular clothes. This keeps the most fragile stuff on my person, and the relatively sturdy stuff gets some padding to protect it.
When I shore dive, I put my computer, regs, and drysuit in the back seat of my truck. I strap the tanks down tightly in the bed. Everything else gets thrown in a giant heap in the bed, and I don't really worry about it. That stuff's hardy, and unless I crash, it will be fine. If I do crash, I don't really care if my fins or flashlights get run over or fall off a cliff or whatever -- at that point, I've got bigger problems
