Since you cannot just go toilet anywhere, even on an island by yourself, you will have to do your stuff in certain areas you have designated for doing stuff.
You may think that digging a hole & doing your stuff in the hole is good enough, but after several years you will find your self running into your old stuff everywhere. Digging every time to need to go toilet will also strain you physically. You’ll end up ruining your digestion & end up digging every 15 minutes, becoming a cycle of bad gas pains.
Since you live on a tropical island & maybe volcanic, let’s learn how to make a seismic toilet. Seismic toilets are good because the constant seismic activity will regularly dispose of your stuff.
Let’s start with the simple 2-plank.