Keen Eye Trophy
Open 50 hidden caches.The location of each hidden cache is randomised each time you load a mission so I can't give you any precise locations but here's what one looks like:
In case the image doesn't show for some reason, hidden caches look just like the standard supply crates except they're orange instead of grey/brown. Fortunately, you get to keep the contents of a hidden cache if you die or fail the mission.
Please see this video by MrReign, which shows the potential spawn points of each hidden cache:
Also, see this video for a sort of farming method (credit to WheatYT): LINK