I'm personally no longer in favour of counting mundane ammunition for ranged weapons. I find the realism benefits for the bookkeeping costs aren't really worth it, and in practice many players may tend to 'fudge' anyhow. So I now prefer the Warhammer Quest 'you have enough ammo for one...
I like SweeneyTodd and Hypersmurf's approach.
If we see RPG adventures as 'the players and GM create a heroic story together', then once-a-day or once-per-encounter powers can be seen as player-based story powers to influence the in-game story, similar to Force Points, Fate Points, Destiny...