I think this is how it works, but you may want to check the wiki for details:
The mod loads resources by looking in an approprieate txt file for references to where the resources are stored. The resources should be stored somewhere in your mod's folder in a subfolder or something. You need to:
a) get the right resources you want and
b) write up pointers to your stored resource files in the right txt file.
The template mod that comes with the game only has a few example resources (a few entites, a few tiles, etc). If you want more, you have to get/make the files and write the txts yourself. Unless you get a mod that has all the resources already and you edit it (as Alec suggested, The Bear's ones I think are the most complete for that).
Maybe someone should make a new template mod that has all the resources from the game with a blank map like the current template mod? (If it doesn't already exist lol, I might not know about it).