try this
on *:text:!milk:#:say hands $nick a cool glass of milk.

if you are planning on having many drinks added you wont want to do it quite like that
Code:
on *:text:!drink *:#:{ msg $chan hands $nick a refreshing glass of $2 $+ . }

more optional:

on *:text:!drink *:#:{
  if ($2 == buy) {
    msg $chan here is a refreshing $4 $+ $chr(44) $3 $+ . On $nick $+ s tab.
  }
  else {
    msg $chan hands $nick a refreshing glass of $2 $+ . 
  }
}

that will respond to !drink buy name drink
like !drink buy sue cola
resonds
<botsname> here is a refreshing cola, Sue. On mmoshkins tab.
or
!drink beer
<botsname> hands moshkin a refreshing beer.