My own Personal Autoexec i worked on for the past Years.
Each Category and Command should have their explanations if necessary and is easily customizable or expandable by executing your own configs.
Download the Repository as zip here.
Move both the autoexec.cfg and the configs folder into the cfg folder of your game.
Default Paths:
Windows: C:\Steam\steamapps\common\Left 4 Dead 2\left4dead2\cfg
Linux: /home/user/.local/share/Steam/steamapps/common/Left 4 Dead 2/left4dead2/cfg
*Note: If you play under Linux i would recommend setting up a Wine Prefix with the Windows Version of steam and L4D2 as the native version is known for crashing.
Recommended Launch Arguments can be found here
Recommended Video Settings can be found here
Anything else should be self explanatory or explained in the config.