give rifle - Arms you with the Mk 47 assualt rifle
give pipe_bomb - Gives you a pipe bomb
give propanetank - Gives you a propane tank
give oxygentank - Gives you an oxygen tank, which acts similar to a propane tank
give gascan - Gives you a gascan, yet another flammable item to carry around!
give molotov - Arms you with a molotov cocktail
give first_aid_kit - Gives you a first aid kit
sb_friendlyfire (1/0) - Control whether or not bots do friendly fire damage
You could always go a different route, where instead of outfitting yourself to be more capable, you modify the zombie apocalypse to make it easier to handle. With the codes below, you toggle zombie health, turn off rushing mobs, or get rid of zombies altogether. You can also spawn additional zombies and special infected if you're looking for more of a challenge.
z_spawn mob - This will spawn a zombie horde
z_spawn (special infected) - Enter tank, smoker, hunter, or boomer in the brackets to spawn that special infected in your crosshairs
z_health - Allows you to toggle zombie health
z_common_limit - This sets the maximum amount of regular zombies
director_force_panic - Sets off a panic event, in which zombies rush you
z_speed - Toggle zombie speed
z_spawn zombie - Spawn a single zombie
tongue_range (#) - Put in a number to set the smoker's tongue attack range. Default is 750.
director_stop - Turns off all wondering and rushing zombies, as well as specials and bosses
director_no_mobs (1/0) - Turns off mob rushes
z_tank_health (#) - Input a number to set the maximum health of the Tank
Some codes simply exist for fun with no direct effect on gameplay. If you type "thirdperson" into the console and hit enter, the camera will position itself behind your character for a third person view. If you want to change back to the default view, use the code "firstperson."
There's a lot of potential here in these Left 4 Dead console commands, so experiment with all of the additional settings until you create a gaming experience that is perfect for you.