There's a difference between "fit" and "fit without making it impossible to walk normally". And really, you'd want some sort of carrier for the cards, because otherwise they're likely to be lost or damaged. So it becomes a fairly complex question of the optimal balance among total carrier volume, gait effects, and maximizing internal volume of the carrier without thinning the walls so much they're likely to crumple. (Metal walls might serve, but then we're back to gait effects. Not comfortable.) And once the carrier design is in hand, there arises the question of how to maximize its bandwidth, which is itself a rather nontrivial packing problem.