More often that not, a keyboard will have extra functionality keys that you can bind to different operations.  Xbindkeys makes it easier to make each key perform a specific task.

First, run “xbindkeys -k” to determine the code for a key.  For example:

"Scheme Command"
m:0x0 + c:160
NoSymbol

Then change the “Scheme Command” section to the command that you want to run when the key is pressed.   For example:

"amixer set Master 5%+"
m:0x0 + c:176
NoSymbol

Place your newly created command in ~/.xbindkeysrc and add xbindkeys to your ~/.xinitrc.