If you just want unit to drop random item on death, do following:
Create a array of item-type (Ctrl+B in Trigger Editor, create new variable of item-type and mark it as an array), and add this to initialization trigger (with Map Initialization event):
Events
Map Initialization
Conditions
Actions
Set xxx[1] = Gold Coins
Set xxx[2] = Scroll of Town Portal
...
[xxx is a name of your item-type array, create as much elements as you wish]
Create new trigger:
Events
Unit - A unit dies
Conditions
(Owner of (Dying unit)) = (Neutral Hostile)
Actions
Item - Create 1 xxx[(Random integer between 1 and x)] at (Position of (Dying unit))
xxx is your item-type array and x is count of its elements.