Redone - Find three game features built on top of the above game mechanic

Three game features that are built on top of collecting:
1- Levels/ missions
2- Progression/ unlock-able 
3- Accumulate items

Levels/ missions: 
Levels/ missions are what make a game some what complete because then it gives you something to strive for, a goal to reach, a meaning to the game itself. A good example of collection in terms of levels/ missions wise is if you collect as many items in the game you pass the level, or if you collect a certain amount of kills you complete the mission.

Progression/unlock-able:
Once you collect an abundance of items you gain value which can unlock items that you may need in future tasks. An example of collection in terms of progression is that is you collect a certain amount of XP (experience) you can gain levels and unlock more gear/ tools that will help you in future game play.    

Accumulate items:
An example of accumulating items are for example in Super Mario bro's, collecting coins and if you accumulate a certain amount of coins you gain a life and accumulating coins is the aim of the gain. Another example is in Age of Empires where you collect food,gold,stone and wood to create bigger and better things(units/buildings) for your city to defeat the enemy.