The note on this polaroid has always stuck with me. "No phosphorus grenades".
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Does the note mean they never made it to the set? Does the note mean that she has them (the belt tools) and they should be taken off (even thought they stayed on in the film).
Either way, it means that phosphorus and the ability to 'pop smoke' was in someone's mind in the costume department. To me this has to be near the top of the list for the belt tool's true purpose.
2nd place in my mind is a battery pack. Pulse rifles need to keep up their electronic pulse, motion trackers need to keep sweeping, shoulder lamps need to keep shining, and the shared body/foundation for the smartgun battery can't be ignored. A universal battery that could recharge any of their field equipment makes too much sense to be ignored.
Definitely one of those two in my opinion.