What rewards can you get from each chest?

The bigger the size of the chest and the more valuable the material, the more rewards it will contain. These are the rewards you can claim from each chest:

Each week, you can get tons of rewards by completing the Community Challenge with the rest of your team. The rewards that can be claimed from the Community Chest will depend on two factors, the size and the material of the chest. These will vary based on how many points each player obtained individually and how many points the whole Community won as a team. 

The size of the chest can be XS, S, M, L, XL, or XXL. It will depend on how many points the Community obtained as a team:

The material of the chest can be Bronze, Silver, Gold, Diamond, Ruby or Emerald. It will depend on how many points are collected individually by each player:

For example, if a player obtained 15000 points and their Community as a whole collected 28000 points, the player will unlock a Large (L) Gold chest. 

More info about the Community can be found here.