An "ashplant" is a walking stick fashioned from an ash sapling that has been cut off below the surface of the soil, supplying a natural handle.  Stephen may have begun carrying his for protection against dogs, but he thinks of it as also possessing various kinds of magical power.

John Hunt 2017

A rustic ash walking stick. Source:

An Etruscan lituus instrument, from the Dictionnaire des Antiquités grecques et romaines de Daremberg et Saglio. Source: Wikimedia Commons.