EX: Shounen Hyouryuu

This is a very enjoyable, albeit short, shipwrecked/apocalypse/survival manga. Like most shounen manga of this variety, almost all of the "good guys" are teens whose biggest enemy are adults, but this one is quite enjoyable. Although I wish it was a bit longer, it still has a good ending (which is better than a drawn-out manga, in my opinion).

It's good if you're looking for something that can be read within a day, and you're not looking for anything too deep or powerful.