hi there,
this method is a glitch/bug/exploit (like from the original Dead Island).
with this you can duplicate every item. i've used it for my last two levels (68->70).
the requirements are the same as in the above solutions. you need the "endless missions" (where you bring the food cannes, knives, bleach, ....)
go to a place where you spawn directly, when you use the "load last checkpoint" option (i've done this in a safe house)
- go to your inventory
- search for the item you want to double (like bleach)
- drop this from inventory
- walk some steps away and use a grenade to kill yourself (now it's important that you hit the start button when the screen turns red)
- use the "last checkpoint" function
- when you respawn, the items you've dropped are still there
- collect them, and do it over and over again, how often you like.
i duplicated round about 200 bleach. then i went to nina in the hospital and gave her the bleach. with every bleach you'll get round about 50k exp and 2300 credits.
p.s. credit goes to A Spiderpig
sry for my bad english ;)