Where going MINECRAFT bois!!, It's great that he made those primitive tools and now it will make things much more better and easier, next thing that they have to do is to ensure food in case of weather issues (Which is what they are doing) after that, They should make furnitures first like beds or cover for the floor when they are sleeping, A good material to use is Coconut leaves, one step at a time, progress easily but do not rush things out and think of what is more important in your current situation, After that...find a way to gain help from the outside and continue surviving inside the island.
Side Comment: I do not trust a single girl in this manga, This newcomer? I am sure that she's a spy from those bastards since this bitch is observing them...Besides it's not like those bastards will just keep quiet right? They did mention that in the earlier chapters so it is not impossible, Remember that he was treated and bullied back in their School...As i said in the past chapters, Do not let your guard down...You don't know the motive of this bitch and you should think on how the fuck did she survived for days? Being cautious is one of the things you need in surviving...Keep in mind that you have to be the Apex Predator not the Prey.