Base cost: 2 CP PLUS usual costs for whatever you put in it.
It has to be something that a minifig will reasonably be able to carry in his or her hands - no vehicles allowed. Just general weapons and small handheld items.
Searching the case for a specific item that the player has put into the case and paid the CP for is a whole action. The minifig spends a whole action searching the case for a specific named item.
1 - critical failure: The case breaks and all the contents are spilled around it in a 2" radius. The case is FUBAR, and anyone nearby may pick up items as they are on the ground and free for the taking. This includes minifigs of opposing players if they are close enough.
2-3 - failure: The minifig fails to find what they are looking for. Better luck next turn.
4+ - success: The minifig finds what they are looking for and can equip themselves with it, ready for their next turn.
Critical Success [natural 6 on a d6, natural 8 on a d8, natural 10 on a d10, etc]: The item is found so rapidly that it does not take up an action and the minifig can use it immediately as if they already had it in their hands.
A minifig with a "Basildon Bond's Spy Briefcase" can also put any hand-sized objects they come across into the case. Retrieving them again is done through the usual dice roll.
Size limits: Anything that is listed in the rules as a standard weapon or piece of equipment in the "Mighty Minifig" section of the rules can be put into the case. Anything that is made through the creation rules. including larger weapons, are considered too big to put into the case.
In theory one can have a whole arsenal within the case of standard weapons, armour, and other bits of assorted equipment. Tardis Theory is in play here, within the limitations set out above.