This guide based on this video:











So, credits goes to Senor Meowzors

Warning.
I'm used it only in SOLO-game and not tested in COOPERATIVE. Obviously...

In folder:
C:\Users\Your_user_name\AppData\Local\Activision\CoDWaW\mods
Make a folder with random name. This will be name of your mod.
for example: "Deathcards"
It will look like:
C:\Users\Your_user_name\AppData\Local\Activision\CoDWaW\mods\Deathcards

Then make folder called "maps" in it
It will look like:
C:\Users\Your_user_name\AppData\Local\Activision\CoDWaW\mods\Deathcards\maps

Download or copy file "_collectibles.gsc"[pastebin.com]
Be shure the extension of file is ".gsc"

It will look like:

Go in Steam Library and call properties of Call of Duty: World at War by right click on it, and then click "SET LAUNCH OPTIONS".

Write this line:
+set fs_game "mods/Name_of_your_mod"
We used "Deathcards" as example, so it will be:
+set fs_game "mods/Deathcards"

The easiest part is done.

Now start Call of Duty: World at War

Be shure you enabled console in options menu.

After that, you need to figure out what deathcards you want.

Make a COOPERATIVE game and setup the deathcards you want to use.
(all deathcards console command: "cheat_items_set1 99999999999999999")

After you've done that, press the tilde key (~ key) and type in "ui_hostOptions".

Remember the number.

Back out of the host match screen and click on SOLO instead.

Before choosing any of the maps, open your console and type in "ui_hostOptionsEnabled 1" and "ui_hostOptions xxx" (replace xxx with the number you remembered).

Load the map and it should work.

Profit!

Sadly, the DLC zombie maps don't work.