The Hardrock has rack and fender eyelets at the rear but not at the front. (The Stumpjumer above lacks these useful features)
Fit a standard rear rack that bolts to the frame.
I would suggest a pannier with modern quick-release locking hooks rather than velcro or hook and elastic. Make sure the panniers fit to the racks.
The Hardrock can accept a bolt-on rear fender such as SKS chromoplastic. These come in F/R sets. The F one will not fit unless you get some kind of bracket to the suspension fork. Most people fit clip-on fenders which are not so effective.
The Hardrock is a bit heavy at the front due to the fork. You may want to consider switching to a ridgid chromoly fork with fender eyelets (eg Kona Project). Some older bike shops have used forks kicking around in corners.

Get some good quality commuter style tyres. Puncture resistance will prevent you being late for work, which is more important than ultimate speed. For snow , normal MTB tyres are good but for ice, they are not good enough. You can buy studded winter tyres or make your own. My DIY studded tyres worked well and didnt cost much.