H&K G3A3 (More specifically AG-3F2 with all the bells and whistles). You will want something with a heavy round as I would suspect 5.56 Nato rounds wouldn't really do much to something that is already dead. The good thing about having a heavy weapon with a bayonet is that you can hit them with it too.
If I was going fantasy I would say light saber.
A Fubar
http://www.stanleytools.com/default...y®+Fubar®+Forcible+Entry+Tool+-+30"
Functions as a crowbar, wrench, pickaxe and hammer (yeah, ive thought about this scenario while down the builders merchant lol).