Cactus was the designation for Guadalcanal until 1943. For example, the air contingent was nicknamed the "Cactus Air Force." Sadly, I don't know the other islands, but I would conjecture that some of them would be from the same naming scheme.

Allright, this looks fun. As Domini pointed out Cactus is Guadalcanal.

Bouraille could be Bourail which is in New Caledonia. The Plaine Des Giacs airfield is also there(http://en.wikipedia.org/wiki/Plaine_Des_Gaiacs_Airfield).

Flattery is the Cape Flattery Military Reservations(or air field near by) http://fortwiki.com/Cape_Flattery_Military_Reservation

Buttons is a dump/Base on Vanuatu. (http://cabinetmagazine.org/issues/10/million_point.php)

Sand island could be the hawaiian one with the base. Not sure about rest.

EDIT: I totally had a dream about fighting in the Pacific theater tonight, which I think is my brains way of telling me to finish this. So I read the journal again and the part where he mentions Tentona(tontona) has some obvious clues. He states its a Ferry base and about 3 hours away from Vanuatu. Looking at near by ferry bases I came across Tontouta Airfield in New Caledonia. (http://en.wikipedia.org/wiki/Tontouta_Airfield)

As Aurevir pointed out Frisco is probably San Francisco especially since there is a Fort Mason there, and Ifacti is Efate which indeed had a base called Roses.

Kulsoa is tricky. Hilo and Hickman are both bases in Hawaii, and he states this Kulsoa is the shipping point to Midway. So it would make the most amount of sense for this Kulsoa to be in Hawaii as well.

EDIT 2: HELL YEA. Figured it out and it was tricky. So he says he was stationed with the 72nd bomb squadron after this mystery base. If you where they were stationed during June of 1942 (http://www.afhra.af.mil/factsheets/factsheet.asp?id=10524) You can see it was Bellows Air force base in Waimanalo, Hawaii. Not to far from this base is the Marine Corps base located at Kailua, Hawaii. It's a stretch. But the only thing that seems plausible.

The only one I know off the top of my head which hasn't been mentioned is Frisco, which is a nickname for San Francisco.

Reading through the rest of the journal for anything to help with, I'd guess the "jui jutsui" from August 2 is probably jujutsu, also known as jiu jitsu. It's a difficult term to transliterate if you aren't familiar with it, which I doubt many people were in 1942.
August 5, "depth chargers" ought to be depth charges, which are antisubmarine explosives.
For October 9, it mentions "155-105 ? 75 artillery"- these are bore measurements, in millimeters, so you have 155 mm guns, 105s, 75s, etc.
November 13, elevators are the horizontal flaps on the tail of the plane that control pitch.
November 27, a gas dump would be a stockpile of fuel- probably aviation gas, given the context, but could be regular gasoline or diesel for vehicles.
November 29, Washing Machine Charlie was a collective name for a series of solo Japanese nighttime bombing attacks on Guadalcanal. They were intended more to keep the men awake then to do any significant bomb damage, and the name refers to the droning noise of the bomber circling overhead.
December 16: "one engine on our plane ? run away prop and was feathered" means that one of the engines was suffering a mechanical defect that apparently was causing it to reach excessive RPMs- feathering it refers shutting down the engine and rotating the blades of the inactive propeller (prop) to be parallel to the wind instead of perpendicular, to reduce drag.
March 28, not familiar with any California WWII air bases, but a quick search yields both Hamilton and Hammer as names for army airfields which could be referred to as "Ham".

"Ifacti" is probably the island of Efate, about 600 miles from Suva.

"Esperanto de Santos" is surely Espiritu Santo, the largest of the Vanatu islands (and the home of the musical South Pacific).