I think I prefer the handwaving version versus having to track each meal. It'd be the way wealth works in some games; instead of having a number that goes down as players spend, you're arbitrarily saying that they can afford (in general) such and such standard of living, and you only invoke cash for items that provide in-game benefits e.g. equipment, consumables that buff combat performance, tools for crafting equipment.

You could have two versions of RadAway to account for the differences: the Instant RadAway is really an emergency field treatment to purify the body of recently suffered radiation (like from rad-scorpion bites) and won't do anything for long-term radiation exposure; the IV RadAway is something they need to administer over time e.g. overnight, and purges the body of aforementioned radiation.

But don't you already have Fallout campaign rules you've used in the past?