bindsym XF86AudioRaiseVolume exec "pactl set-sink-volume @DEFAULT_SINK@ 5%"
bindsym XF86AudioLowerVolume exec "pactl set-sink-volume @DEFAULT_SINK@ -5%"
bindsym XF86AudioMute exec "pactl set-sink-mute @DEFAULT_SINK@ toggle"
Then, connect the keyboard's USB dongle and you're done. You're controlling volume.
That said, you can program those same volume buttons to open a terminal and display
cowsay
if you want to.