First go through and clear an area of enemies, then grab (Click the right analog stick) a 55 gallon drum. If you are having trouble carrying with over-encumbrance, this cool trick could help you tote around some extra gear. I don't know if this works with any other follower. Go back to Underworld where you first hired Charon. After a while it should appear, 'Charon gas returned to the ninth circle'. Fire him before freeing Fawkes from Vault 87.