At the 'Main' menu select 'Advanced' followed by 'Enable Developer Console' and type 'sv_cheats 1' (without the quotes) when the console window appears to enable cheat mode when 'Create a Server' is selected. If you now enter the following codes at the console window the corresponding effect will become enabled.
Increase Number of Items you can Carry:
Type 'inv_maxcarry (number)'
Mimics Spectator Mode:
Spawn ALL Weapons:
Type 'impulse 101'
Easy "One Free Man" achievement:
Crowbars are common melee weapons that are found in various locations. Drop your
current melee weapon and collect a crowbar when one is found. To easily kill
zombies with it, hold the Mouse Button for a few seconds and aim for your target's head. After any hit with the crowbar, quickly press V to shove it away to avoid getting grabbed.