autoexec.cfg is the name of the config file where you insert commands (without the preceding forward slash) to be automatically executed when the game starts up. You can use CubeScript in this file. It's located in the folder named config inside of your AssaultCube directory.
Everything you enter here (such as bind commands) will overwrite what is in saved.cfg. To revert to the default configuration, delete your saved.cfg and clear out your autoexec.cfg. When you run the game, a new saved.cfg will be created.