Marines on Guadalcanal would be armed with M1903 Springfield rifles, Reising Submachine guns, BAR's, M1928 (20,30, or drum magazines) or M1 Thompsons and even some British Boys anti- tank rifles in the Raider BN's. (The Boys Rifles where actually used during the raid on Makin by the 2nd Raiders to shoot Japanese seaplanes)The 1st Parachute Bn would also have the Johnson Light MG's and a few Johnson Rifles. After the Army landed on the Canal in Oct '42 some Marines were seen to have M-1 rifles obviously "borrowed" from some soldier when he wasn't looking. No carbines.
Helmets would be devoid of camo covers but some Marines adopted the Japanese "fishnet" covers. Some Raiders also had a burlap cover covered with strips of burlap. I've spoken to one Marine veteran of the Canal who showed me photos of his gun crew and 2 of them where wearing the M1917 helmet. Photos also show some wearing campaign hats and sun helmets although I doubt they would wear them in combat.
An excellent source for Marine Corps equipment in WW2 is a book titled Grunt Gear by Alec Tulkoff. I believe it is out of print and expensive but worth whatever the cost if you can find one. The book, Into the Valley, by John Hersey contains some excellent drawings of Marines on the Canal by Marine artist Major Donald Dickson.
Good luck!
Mike Stelzel