Regular Army - M-14s until around 1968, when M-16s begun phase in. Model 1911A1 .45 cal. was the standard issue sidearm for officers and radio humpers, but many troops carried .38 cal. Smith & Wessons (frequently stainless steel) as well as various shotguns, hand grenades, bayonettes, knives and "pop" flares. Personally owned weapons were officially frowned upon, but .44 Magnum revolvers and autoloaders were not unknown.
Tankers also carried .45 cal. M3A1 grease guns, and the occasional .45 cal. M1A1 Thompson sub-machine gun. In Vietnam, M-1 Garrands and M-1 Carbines were plentiful among ARVN toops, though not authorized for US Army personnel.
Carried at the squad level were 7.62NATO M-16 machine guns and M-79 gernade launchers. Oh, and lotsa ammo.
National Guard - anything from 09 Springfields, up to the latest M-16s, depending on what was in the State armory.
USMC - Hey!, I'm not givin' up any secrets about what we carried.
Phil