You can hand pick the bags that you see before they hatch. The more you pick off now the fewer there will be later on. The eggs will hatch in late May or June and you will probably need to start your control measures around that time and continue until you don't see any more damage. You can use Bt, Spectracide Triazicide, bioneem or any insecticide that lists caterpillars on the label. Since you have some time while you are picking off the bagworms, look up the product labels on the internet to see what the product covers, how long it lasts, how to apply it and precautions that will be necessary to take. Always read and follow the label instructions. Bt (sold as dipel or thurgicide ) are probably the most specific for caterpillars. It is applied as a dust, but it is active against caterpillars not the eggs. So, for now the best bet is to pick off as many of the bags as you can and destroy them.
Happy gardening in Hawaii. Gardens are where people grow.