I wouldn't be surprised if we get pretty ambitious mods adding stuff like fuel, ammo etc to "equipment" which means you'll have to produce that stuff as well, depending on if the AI can handle it of course. We were never bothered with stuff like ammo in HOI3, it was an integrated part of supplies (which we still have, we just don't produce it in HOI4, just balance on-map capacity).
The bottleneck for ammunition of various calibres was never really a strategic problem production-wise for most nations in WW2, the problem was logistics issues meaning the frontline units could get into trouble, so I'm pretty fine with stuff like that abstracted through the jerrycan icon and bundled with the supplies.