What I did:
1. In the Shoot.cs script, create a function that will add 50 ammo;
2. Then I created a new script on the collectible object called "GivePlayerAmmo"
3. In the GivePlayerAmmo.cs script, make a onCollisionEnter function.
4. Also in the GivePlayerAmmo.cs script, make a public GameObject variable where the "robot" will go.
5. In the onCollisionEnter function...If the tag of the other object is a player...
5.1. Destroy this object.
5.2. Use this to add add ammo: robot.GetComponent
Type the number of keys you want to be disabled and then press ENTER.
I have 3 keys to disable so I typed 3 and I pressed ENTER.
NOTE: If you get weird numbers like if it goes from 4, to 2, to -3, to -8, etc. This is because the keys are put too close to each other and using the GameObject.Find() function is slow so it takes time to update everything.
To fix this, wait a little bit between collecting each key, or place the keys further apart so the player will spend more time finding keys.