The M-1910/-1923 cartridge belt had ten pockets, each capable of holding one 8 round clip, so that's 80 rounds on the guys belt, plus a clip in the Garand.
Period photos show GIs most often wearing bandoleers, either one or two, criss crossed over thier shoulders. These, from what I've read, held six clips apiece.
According to Eugene Sledge's excellent memoir "With the Old Breed", Marines in the pacific were resupplied with a so called "daily load", that consisted of 100 rounds of .30 caliber ammo for riflemen.
Also, in some photos, you see guys with a couple of clips stuck in the sling of thier rifle, however, in my reading, that was a great way to knock the rounds out of alignment or get them dirty before loading.
Also, in Stephen Ambrose's "Band of Brothers", some of the photos of the 101st paratroopers are shown wearing normal pistol belts in lieu of cartridge belts, while being armed with Garands. These guys most often wore bandoliers and had pouches made out of spare canvas from guys in the parachute rigging shop.
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