(Person 1): "What did you get in your care package from home?"
(Person 2, happily): "Military-grade explosives!" -- TheDragonsFlame
The weatherproof box said 'Plasticine' and contained some ridiculously disproportionate cartoon characters on it. Inside were wax-paper wrapped blocks of brightly-coloured stuff that one might expect to be plasticine. But, to a non-casual observer, it wasn't... quite... plasticine.
It was amazing that the guards let it past, to be honest. But then again, Monty and the boys had been spending months on putting the goons to sleep with the sheer monotony of their "good behaviour". They probably didn't even bother looking beyond the wax paper. Just like they didn't know about the maps that came in via playing cards or the more elaborate ones concealed in board games. Or any number of little treasures that they hid in any number of places.
That's what they got for putting "all the bad eggs in one basket." They got the most devious, devilish, and determined escapologists tying up enemy resources. People who could make a pair of wire cutters out of an empty bully beef tin and have three escape plans before the goons finished ushering them into the camp. Bad eggs like them could keep the enemy scrambling for some significant time with this stuff.