I realize clips and enblocs for some rifles were discarded, but if a soldier shot all the rounds from his M1 Carbine, would he drop the magazine on the ground or save it? Did this change in later conflicts?
To answer your comment specifically for the M1, Field Manual 23-7 clearly envisions that the soldier must maintain his magazines for reloading. Pages 13 and 15 of the linked manual describe the care a soldier must take with his magazine to ensure its continued desired functionality. Page 22 describes the process of loading the magazine. Page 75 states that all magazine are inspected prior to leaving the range. Pages 28 and 29 deal with how ammunition should be handled prior to firing. The lack of similar instructions for the receipt of a large quantity of magazines indicates that an infantryman was supposed to maintain his own magazine, preserve it after it was empty and reload it himself from an ammunition depot. This index of field manuals has those for several other weapons used during WW2 but the links are dead. If you google the number of a particular field manual (say "FM 23-7") with the term "pdf" you should find other copies of it on the information superhighway.