Write SOS, then begin Castaway fantasy. If help arrives before you've had enough, ask if they could please come back and rescue you in a couple of weeks because

Write SOS, then begin Castaway fantasy. If help arrives before you've had enough, ask if they could please come back and rescue you in a couple of weeks because you're trying to build a treehouse or setup irrigation channels for basic farming and you haven't even managed to spear your first fish yet.