Could you be a bit more precise? Are you concerned about multibasing vs. single-basing, or are you looking for textures to use?
If the latter, I'd suggest using a mix of rather fine sands and gravels (quartz sand, for example), to represent "islandy" ground, with some tufts of vegetation. For the volcanic isles such as Iwo Jima, I'd suggest painting them ash colour, obviously, and omit the vegetation.