I interpreted the phrase "saving missiles for a future mission" to mean thus: if you don't use the missiles, then they are added to your ammunition in the next mission. For example, if you had six missiles, and finished a mission with two of them remaining, then you would have the extra two the next time, and could thus launch with eight missiles. This was not done in Wing Commander because each fighter was given a maximum missile capacity--you launch with every missile mount already full on most missions, and there isn't anywhere on your fighter to mount additional ones--if there had been more mounts, then you would already have had them filled to begin with. Thus, you always fly your Hellcat with six missiles, because six is all that it can carry.