So now, when killing a monster, they have a probability to drop one item (coin, ammo). The randomness is quite simple in this first implementation but i will polish this later because for example, i need to be sure that if some ammo are dropped, that the player has the right weapon for this type of ammo.
As i said later, i prefer to implement now the basis and polish everything later.
Next step? Changing map with a door or a stair! But i know this will require lot more work that the last things i have shown.