A horse-mounted figure (or a set of normal animals like horses, bears, wolves)
A vehicle of some sort (a wagon and oxen? horses and a carriage?)
I'd like to see horses with mounted half-figures, male and female. That way you can cut your favorite bones figure at the waist and glue it to the horse for voila a mounted version of your favorite the bones figure.
A wagon or carriage designed in such a way that you can convert your favorite bones figure to stand or ride within would be equally awesome.