Depends on the building but maintenance can cover a lot.
In my co-op it pays for:
-All utilities: heat, hw, gas, electric.
-Property taxes apportioned to your individual unit.
-The staff: 24 hr Doorman, porters, maintenance men, coop attorney, management company.
-Common areas: electricity and maintenance of elevators, hallways, laundry room, community room, landscaping of garden.
-Rainy day fund: account for big projects like roof replacement.
-Underlying mortgage - yes you probably pay two mortgages of your co-op - one for your unit (if financed) and one on the building itself (the mortgage it took out decades ago when tenants bought it from the landlord going from rental to co-op).
-Parking: most bldgs dont have this. Mine does.
-Basic cable
About 55 percent of my maintenance is tax deductible due to the property taxes and interest on the underlying mortgage. Depending on the year, my tax refund can cover three months worth of maintenance.