Hold a Better Ski Edge when required on icy and firm slopes...
Grab yourself a pocket diamond file / stone from your local ski shop.
This handy tool comes in useful for removing those little burrs that
build up on your ski edges when skiing all types of snow, mainly hard packed ski slopes or the odd 'rock' or 'branch' that you may hit, causing the ski edge to loose it's clean side.
The diamond file stone, when run along the ski edge at 90 degrees by 'hand' removes the burrs and sets you up for better grip when needed on the odd hard packed slope.
Good edges will assist you on hard packed slopes but venturing off piste is another ball game altogether.