if you did it correctly, in the .big file alot of the entries should look like this;
Data\INI\Object\ModsFolderHere
Some of the others, such as Weapon.ini or Armor.ini, should look like this;
Data\INI\Weapon.ini
Models and Textures should look like this;
ART\W3D\RandomBigTank.W3D
ART\TEXTURES\SprayPaintHappyFace.dds (or it could end in .tga, depending on what they used)
Other than stuff that begins with Data or Art, im not sure what can go in .big files. as far as i know, anything the game needs that is usually in a folder can be put into a .big file.