Missiles, rockets, and torpedoes, to be precise.
I never seem to run out of them. I assume, then, that they are not limited in terms of ammo.
Seems to me it would make all of these weapons more interesting if they were perhaps more damaging*, but if ships contained fewer reloads for them. ( *depending on the missile in question, and how limited ammo would work balance wise).
Cruiser weapons might have more shots than frigates, and fighters might only carry a handful at most (the more powerful, the fewer).
Having the game keep track of expendable ammunition would create some really interesting (in a fun way) problems to solve in ship design and tactics. Anti-missile point defense would become more critical since letting a missile through would be more dangerous. Fighters could expend their ammo, then they RTB (as if damaged under “cautious” orders) and reload.