This is rather extremely easy. There are many ways to achieve this, but in the demo, you'll see each event has a death status page. I'll create a new event in template map called Reward, which when picked up will increase 1 Potion.
Now on the death page of each enemy, simply spawn event Reward and that's it. Now when enemies die, they'll create a reward item.
With this method, you can have each enemy to spawn different items. Combining with localPercentages and localVariable conditional branch, you can create a system where sometimes it'll drop different items.