People may visit when you are not there. In the US, the shoreline up to some strangely defined highwater mark (which is higher than you expect) is public. Canada has a similar deal related to crown lands (you may own the island, but the bit under the water, not so much). These visitors have every legal right to hang out, have a picnic, play jarts, whatever.
When you aren't around you will get more visitors. (I have pretty good camera surveillance, mainly to enjoy from afar, but I also get to see the visitors.) These will be bolder and walk around and look at the place.
If you aren't around and the local environment is right, you may get hunters. We get duck hunters and goose hunters. We generally give a few people we know permission and kind of rely on them to discourage anyone else. Hunters are territorial. One year it was posted with "No Hunting" signs nailed to the dock, but not by us or anyone we know, a good attempt by a hunting hacker to secure himself a private hunting area.
Have a medical evac plan. I've used mine in weather that I would probably not have used an Amazon boat.
Have a "pinned down by weather" plan with respect to food and water. I know a couple that was reduced to surviving on popcorn and bloody mary mix for a couple days. Also, know when you are pinned down by weather.
A food digesting composter keeps your trash bags from getting disgusting.
If there is cell coverage, but only for odd carriers, consider an "island phone" that just stays there. If there is no cell coverage, get a VHF that can reach some emergency agency.