Its all very different what to with your island troops, depending on where your fronts are and so forth, these lone soldiers also make difficult for the Japanese player to maximize his efficiency.
Okinawa and wake islands (1 inf each) are very easy to pick up, while your massing land troops to Asia from the East Japanese seazone you can just make a move back and forth and have them on the mainland in a single move.
Philippines (2 inf) are usually a first turn pick up for me, this move makes all your trannies go from japan in you next move which makes for more options on where to land japan based troops.
East Indies (2 inf) While heading south for that nice 3 IPCs in India my troops pick up these buddies
Borneo, New Guinea, Caroline & Solomon Islands (1 inf each) these all come a little later in the game, sometimes they just stay, Borneo goes to Asia around 50% of the time, while the others and maybe the Borneo inf, depending on circumstances go to Australia and new zealand. If i head for Australia I usually make few more pick ups while the trannies are heading back to the real fight.
If the US go Island hoping I like to have some defending infantry on my islands, not because its worth it (its not), more because if the US goes for Japan first I’ll have a lot of other things on mind than using these spare troops and they shall not have ANY of my islands for free
Regards,
Daniel