Resource list (Source)
A RES file accompanies a BSP file when the map uses custom content. The RES's filename is the same as the map's and the only difference is its extension which is .res. It contains something like:
"Resources" { "materials/materialsubfolder/material name.vmt" "file" "materials/materialsubfolder/material name.vtf" "file" }

There's a couple of programs out there to help with this:
RESGen is a tool to create RES files for Half-Life: http://www.thezproject.org/projects.php?pid=2
BSP2RES is a tool to create RES files for Counter Strike SOURCE: http://stas.mail15.com
ResMaker: http://halflife2.filefront.com/file/HalfLife_2_CS_Source_ResMaker;34374
www_mapadd.exe Automatically creates a resource file when you compile for custom textures. Can upload both the map and textures to an FTP server automatically as well.: http://forums.facepunchstudios.com/showthread.php?t=227769