That is an extremely narrow reading of the rules. It isn’t as if there’s a physical first aid button that simply stops working when you’re not in combat.
The problem here is twofold - players seeking to “optimise” the fun out of a game by taking reasonable ideas to absurd extremes (it happens with every game) and GMs seeking limits to keep their players from doing that.
Here’s the thing: at no point in my decades of gaming have I ever seen a system that hard-limited how many times you could make a healing skill test (or equivalent) per day that actually made sense - it was always an arbitrary limit to avoid abuse by players “optimising” the fun out of the game. It just doesn’t work.
Part of the reason it doesn’t work is that real-life healing doesn’t work that way. You can’t just put bandages on someone infinitely forever and fill up some imaginary health meter. There’s a context to healing that the abstractions common to RPGs often can’t handle.
My diatribe aside, let’s try to put this debate to rest:
Within Combat healing is handled by specific actions, such as First Aid and Use Chem. First Aid covers immediate trauma care - dealing with wounds as they happen (If you do it an hour later, and it’s the third time you’ve looked at that injury, it isn’t really first aid) - so naturally it cannot be used outside of combat. Use Chem is listed as a combat action because it’s an action which will occur in combat, and most chems have effects which are short-term boosts that are mostly effective in combat.
Outside of Combat what activities you can perform is largely left at the discretion of the GM based on the prevailing narrative (this is the part that’s being overlooked). You cannot typically perform First Aid outside of an action scene, as noted above, because first aid is done as soon as possible after the injury occurs… but if a character takes damage (say, from a trap or hazard) outside of combat, First Aid is entirely justified (at GM’s discretion). Similarly, there is nothing to prevent you taking Chems outside of combat, but we shouldn’t need to spell that out explicitly - it is a thing the character can attempt to do, so they can do it, but outside of combat, the GM may need to adjudicate some specifics. Long-term care (specifically for injuries, as HP are restored fully by rest) is a matter of a medic assisting a patient’s natural healing, rather than the medic doing specific things themselves.
Stimpaks are an awkward item. Strictly speaking, they just restore HP, but in narrative terms they give a kick-start to the body’s own healing mechanisms. In the midst of combat or other dangerous circumstances, they’re great for first aid - those are the times when you need an immediate boost - but they can’t heal you completely (in a narrative sense - remember, the game mechanics are an abstraction), and sooner or later you just need to have something to eat (that accelerated healing would burn calories), get some fluids, rest and let your body get on with fixing itself: just pumping yourself with Stimpaks can’t be healthy. This is why the bulk of healing out of combat comes through food, drink, and rest.
Mechanically speaking, Stimpaks are most useful in combat. They provide either a small instant boost of health (or treating an injury) as a minor action, or a much-enhanced First Aid action. Food can’t be consumed during a fight, and drinks can be but as a major action instead (but most drinks you’re probably drinking for the other benefits - only Nuka-Cola Quantum and Refreshing Beverages provide better healing than a Stimpak in combat).
Outside of combat, only the most basic food items - raw fruit and vegetables, the most common forms of raw meat, most pre-war preserved foods, the kinds of things you can scavenge easily - provide less healing than a stimpak. If you can stop, set up a cook fire, and cook something simple, it’ll almost always provide more healing than a stimpak can. And, at the end of the day, six hours of sleep restores all your HP and lets you test to heal injuries (which is easier if you treated them with Stimpaks earlier). As long-term medical care is added onto rest, it only cares about injuries, because a character who has rested already has all their HP back.
- There’s no actual limit on the number of times you can make healing rolls per day; the limit is based on context. You can attempt a First Aid action as many times as you like in combat, and at GM’s discretion (typically after taking damage) out of combat, and Stimpaks can be used as part of any of those with no limit other than your number of Stimpaks.
- Long-term medical attention is technically an assist on a character’s normal END + Survival tests to heal injuries when they rest; it is not a separate healing test. Stimpaks don’t heal injuries, they just treat them (and treated injuries are easier to heal)
- Stimpaks are not useful for long-term care (because if you’re getting medical attention, you’ve already rested and got your HP back, and you’re already healing injuries, so treating them is redundant).
- Outside of combat, using a stimpak to regain HP is less efficient than eating in most circumstances. It’s allowable at GM’s discretion, but food and rest will restore HP outside of combat much more effectively.