I think "bills" is still used as Jim uses it, as in the terms "advanced
 billing" or "show bill."  That is, Jim is saying that Huck's life as he
 tells it is on the program.  (Compare how Melville talks about fate in
 _Moby Dick_, when he has Ishmael give Fate's program of events as if the
 world were theater.)

 As for Jim's advice to Huck to avoid water because he's going to be
 "hung" (that is, "hanged:" is Twain making the time-honored ribald pun
 here?),
 Jim is using an old folk tradition that those who commit capital offenses
 will never die by drowning because fate reserves them for hanging.  The
 humor in the passage is in Jim's advice to stay away from the water in
 order to make sure that Providence's plan is filled out.  If Huck is
 destined for hanging, then he's SAFE on the water.  Jim thus echoes Twain's
 sense that providence needs as much help from human agency as possible,
 because providence can't be trusted (i.e. doesn't really exist).  Compare
 "Jim Blaine and His Grandfather's Old Ram" in _Roughing It_:
from "Prov'dence don't fire no blank ca'tridges boys," to "A dog can't be
depended on to carry out a special prov'dence."

Gregg Camfield