I'm writing a small game at the moment. Presently, I have one or two design elements that aren't locked down yet, and I wanted to ask for input on one of these.

For dramatic effect, the player's character in my game is immobilised, alone and has a supposedly limited amount of ammo for their weapons. However, I would like to periodically resupply the player with ammo (for the purpose of balancing the level of difficulty and to allow the player to continue if they're doing well).

I'm trying to think of a method of resupply that's different to the more familiar strategies of making ammo magically appear or having the antagonists drop some when they die. I'd like to emphasise the notion of the player's isolation as much as possible, and finding a way of 'sneaking' ammo to the player without removing too much of that emphasis is basically what I'm trying to think of (it's definitely a valid argument that resupplying the player removes it anyway)

I have considered a sort of simple in-game 'store', where kills get you points that you can spend on ammo for your favourite weapon. This might work well, and may also be good for supporting a simple micro-transaction business model within the game. However, you'd have to pause the game often to make purchases, which would interrupt the action, and it works against the notion of isolation.

Any thoughts?