Field and game elements
In the FTC competition, the robot needs to run inside a 12X12 field. Having access to the field and a game element will be super useful to practice and iterate your robot.
The game field is 12X12 field, containing 36 of 2X2 tiles. You can buy the official FTC game tiles from andymark. If you want to save the cost, you can also buy some cheap 2X2 tiles from stores like walmart at the beginning, just to test the robot running on the tile.
Please note, game elements are required. The full field is not required. You could build and test your robot, and later go to another team's field to practice/iterate.