I wish I could say this was my idea but I'm happy to give credit where credit is due and just preserve/propagate/expand it.
Olle Skogren had a proposal in discord recently about requiring expensive material components for spellcasting in ACKS, their prices scaling exponentially with spell level.
This is both meant to make magic a non-free resource, which normally is wasted if you don't use it daily, to differentiate profane and sacred magic [by the different types of components required] and to make lengthy adventures logistically problematic for casters as you need at first backpack space for reagents, then a mule load and finally cartloads.
Emphasis mine - as that was the bit that most caught my attention.
I could take or leave the exponential cost scaling. I think just having material components with mass that you have to haul into the wilderness seems like a super-viable solution to my issues with the spellcasting resource model in the wilderness game , where spellcasters can dump their full load onto any wilderness encounter because you very seldom have more than one encounter per day. Material components are a resource that is attritable on scales of weeks; they create a limit on total spells expended during a particular expedition, without reducing the total amount of spell-power an MU can bring to bear in any one tactical engagement. And they're super-associative; they're object in the game-world, no need to impose wonky spell-point recovery systems that operate differently in the wilderness and civilization, or argue about what constitutes an adventure for purposes of spells-per-adventure. And since they're items-in-the-world, they interact with market mechanics, and their encumbrance introduces tradeoffs around speed vs preparedness.
At the bare minimum of complexity, where all components are an abstracted "spell components" item just measured in weight with a fixed cost per stone (maybe arcane components and divine components), it would not be hard at all to add to the wilderness logistics spreadsheet. And then you could set up the material component costs of spells by level, so that maybe 1st level spells don't use them (so MUs have something always fall back on), and then component-mass required ramps up with spell level. Or set up material component costs per spell, like Wolves of God does with its spellcasting system (I forget what he calls the points expended to cast, but spells of the same level cost significantly-varying numbers of points) - so sleep and fireball could have their high utility balanced by having to expend component-mass, whereas your lower-tier combat spells like burning hands might be free or just inexpensive.
One could, of course, go the traditional / AD&D route, where particular spells had particular components and they weren't interchangeable. This would be an interesting avenue to introduce a layer of Vancian-style planning on top of ACKS' spell repertoire system. And then non-consumed/focus components (like the amber rod and rabbit fur for lightning bolt) dictate how many parallel/simultaneous castings of a spell your collected MUs can drop in a single round. But I don't know that I need that degree of precision to solve my wilderness-level problem.
This seems like the sort of thing where I should jump up and down and yell "Gygax knew!" This is exactly the sort of "crufty old mechanic that nobody uses turns out to be critically important" thing that this blog was started on. Gygax's Fence, if you will. But I'm actually not sure. The 1e DMG's encumbrance section (page 255) notes that material components aren't assumed to encumber unless they're unusually bulky. I guess that yeah, if you're going to have spell-specific components, that would be a lot of paperwork. And then I suppose the limiting factor on number of casts worth of a particular component that you'd bring on a wilderness adventure was cost, maybe? Maybe in the misty dawn era before the shared Google Sheet of party encumbrance, it was hard to get players to actually honestly track it, whereas gold was an easier thing for a DM to keep account of, since you know how much each PC earned each adventure, and you can know how much they spend on each transaction.
But the age of the spreadsheet is come...