What would you do if you're entire high school class was stuck on a desert island?

You're on a cruise ship and it hits an old WW2 naval mine. You basically just have the clothes on you're back and something small on your pocket such as a pocket knife (If you carry one on a regular basis or on travels), a sea salt cellphone, etc. Luckily the island is large and is mostly flat with the exception of a few hills along with a few small islands surrounding it. The island was occupied by Imperial Japanese and the island has lots of guns and a few tanks. So what would you do? Answer honestly please because I'd to get some different perspective.