I hated all the chords for Drummer Boy that I found online so here we go:

   G                Am           Em
Come they told me, pa rum pum pum pum 
A new born King to see, pa rum pum pum pum
   D          G               Am           F
Our finest gifts we bring, pa rum pum pum pum
 D         G                F           Am
To lay before the King, pa rum pum pum pum, 
             Em               F
rum pum pum pum, rum pum pum pum, 
 G                  Am           Em - F
So to honor Him, pa rum pum pum pum,
         G
When we come.