The only left luggage facilities in the main station / bus station are a series of lockers. These are in the bus station on first floor and in the basement at the train station. They are not cheap and cost the same whether for 1 hour or 12 hours.
If you want to leave skis there are some special lockers in the bus station BUT you may have problems if these are cross-skis - they are unlikely to fit in the lockers - especially men's skis!! During normal shopping hours you can take them up to the big store Ahlens in the centre (about 10 minutes walk). 2nd floor there is a luggage store and it is much cheaper!!