Drafting something I wanna write and not sure if I can work it out. Not sure if I'm smart enough to make this actually work. So there are two people stranded on an island. Initial idea is it was a plane crash but not sure if that will work. The main plot issue I wanted to toy with is that they have a generator or battery or something but it has limited use. It can basically be used for one of two things, and only one of these two things. Either it can be used for some SOS kind of purpose (a radio or something), and the other is to start up a motor on a boat to get them off the island. The SOS function assumes they'll get somebody out there before they die, the boat option assumes they will actually be able to reach civilization. I've never thought about this kind of plot scenario set up so I'm feeling stupid about it. Not sure if this is realistic at all but the idea is the shitty two options situation, and how they have to choose one, builds tension to the climax etc.
How long can you make that tension last? They can't debate over it for long or the readers will get bored. The decision needs to get made and then develop tension over whether it will work. Waiting for a response to a blindly sent SOS will be pretty dull. Trying to make it somewhere in the boat will provide many opportunities for tension and action. (Mutiny on the Bounty sequel Men Against the Sea). I fuss over technical details. If it was a plane crash, how do they have a motorized boat? If they use the radio, can they establish 2-way communication over a sufficient distance to reach someone? Can they tell someone where they are so rescue is possible (Gee, I'm somewhere in the Pacific Ocean). Why isn't there enough battery to start the boat AND use the radio for some period of time? If they take out in the boat, what is the expected range with their fuel? Do they have any idea how far and where they need to go to make landfall? You are going to have to show me that they considered these factors logically or I'm not going to be interested.
I think this is an interesting idea, but I also have very fond memories of Jules Verne's The Mysterious Island. Of course, there were five people stranded there, but the book focuses more on how the people survive and thrive on the island. Granted, it turns out that the island wasn't abandoned, so the comparison goes right out the window, but you can still pursue the fact that these two people of yours might be able to make an amazing life for themselves on the island. This would allow you another point of tension: if their life is good enough, do they even want to leave? Just a thought... If you haven't read The Mysterious Island, do so! It's a great book and might give you some cool ideas for your story.
Try watching "The Island with Bear Grylls" on ITV/UK. It's a reality show with a group of people put on a desert island and left to fend for themselves. It might give you some idea of how incompetent most people are when it comes to survival.