Some suggetions:
-Barbarian-like martial art that heavily depend on STR, with ability allow you to buff Stats/Dmg by shouting (similiar to battlecry)
+Bigger shout means better buff, but also lure more zeds to you
-Adding Training dummy, allow player to trains combat skill at home instead of risking their life with zeds.
+Training dummy can only trains combat-skill to level 2
+Can be use as a decoy to distract zeds in a pinch
-NPCs can train you skills, so why can’t you train them too?
+You can charge money (or items) as cost, or no cost at all! (Increase Trust or/and Value)