The basic rifle squad was equipped with ten M1 Rifles, one M1903 and a BAR, plus a rifle grenade launcher and hand grenades. Pistols and carbines were usually issued to officers and support weapon crews. Although not generally a part of the standard TO&E, sub-machine guns like the Thompson, were found at company HQ's and could be issued to troops on patrol duty.
Other units like those found in Cavalry, Airborne, Marines raiders and Marine companies had a slightly different structure as those in the infantry. Generally the heavier infantry support weapons were kept in support platoons with heavier weapons being kept in support companies or independent battalions.
Many thanks to Bob Price (USMC Retired) and Bill Jaffe for their help with the US Marine Company.