Dead Island Walkthrough Part 3: Act 1 - Passport to Life Quest

Talk to Sinamoi and accept the quest. He will tell you he forgot the main access keycard to the lifeguard tower in his room and to go retrieve it. The keycard is in Bungalow #11.

Make sure to also talk to Steven, to receive a side quest - The Lost.

Head out of the room and follow the markers. Head up the stairs. Watch out for zombies waiting on the top of the stairs. Keep moving, towards the big swimming pool. Dispatch of the zombies in the area. There is also a room on the NW side of the pool with lots of loot. Feel free to search other cabins around for more loot.

Talk to Ted B sitting in a pool of blood. Grab the knife nearby.

Locate Bungalow 11 and open the door. There will be undead inside the room, so be ready to fight.

Loot everything you find in there.  Break the door and enter the side toom. You should  find the lifeguard security keycard there. Pick it up and head back to Sinamoi and speak to him. This will complete the quest.