You need jin for this first drop a weapen you want to duplaicate look at it hold in square look at jin still holding square and tap then hold in square again put it in storge and take out realse square and exit storge and keep pressing triangle
On Chapter 4, during the mission where take the truck to the mechanic, after you enter the shop and the shutter closes, go to the back and you'll pick up some ammo. Save your game and repeat the process until you have full pistol ammo.
When you discover river village and you need level 1 picklock go into the hut with the fast travel map and go into the room behind the door to the left of the map and open and get the things from the chests often in the one on the shelf there are good guns for using or selling for easy money
Weapons that have become blunt through use are not completely useless so do not discard them as they can still cause damage by being used as a throwing weapon. If the weapon is worth keeping retrieve it as you will be able to repair it later.
For help collecting some easy money in Dead Island, once you have discovered the Church and the Warehouse and are in the City, go to the Warehouse and get the Hammer and Baseball Bat. You then need to fast travel to the Church and sell both items. When you travel back to the Warehouse, the items will have respawned - you can repeat this unlimited times!
On Level 7, you should be able to get a Diamond from the safe in the Mayor's office. If you go back into the sewers, but then turn round and check the safe again, the Diamond should be spawned back in there again. You can obviously sell the diamonds - so this is a good way to get lots of extra cash.
Dead Island frustratingly only saves at pre-determined points (though this arguably makes it more addictive). To get it to save whenever you like, simply go to the Controls menu and change the layout from Analog to Digital or Digital to Analog. This causes the game to autosave. You can then obviously change the controls back and carry on playing.