Well, as I said, what he would have found was most likely either spare gear or gear for taking someone out, perhaps a prisoner they have deemed too dangerous. The idea of infiltration, if I am remembering rightly, was touched on in both movies. This is originally first from the first Escape, they infiltrated the New York prison out right, and how the team sent in in the second to find Utopia and get back the "Sword of Damocles" did so in a similar way.
Perhaps they are looking for a specific person, or perhaps just looking for those they deem enough of a threat. It is not intended to supplant any other ideas already in play, merely to to be something that can play into one already agreed on. I don't presume to know all details and things, rather that it could cause some "healthy paranoia" that would naturally be in a prison over finding out there is someone there that is not a prisoner.
As for the details of what is in the case, I am thinking perhaps identifying items, weapons, perhaps a sniper rifle, supplies... etc. I don't have to be the only one deciding on that, nor does it have to specifically be those items. It is a very fluid idea, as it also could have been left from an infiltration before the game started, and the items in it could cause a slight shift of sorts in a person or small groups favor as another option on the idea.
Thoughts? Are more details needed?