Do you mean hidden compartments/pockets in one's armor? Because if so, I did something along those lines for the magazine of my SAW. I didn't use a hinge or anything, but instead made a slot for the cover to rest in at the top, and embedded a rare earth magnet to hold it closed. Here you can see the open door:
And here it is closed, after paint:
Unless you look veeeery closely, it looks near identical to the 2mm piece of craft foam that makes the mirror of that detail on the other side of the mag, due to the way I recessed it. Hope this helps!
Also, if you are looking for storage dont forget drop pouches and such can still be an option. Its not even crazy unheard of in canon. ODSTs and Spartans alike have used pouches in the past. Great for cell phones, wallets, etc at the cons.