Here is a list of possible services, typical ones, with their corresponding vehicle, timing and particularities.

Services for arrival flights

Mobile staircase
Coach busses
Baggage off-loading
Cargo off-loading
Cleaning
Sewage
APU
ASU
Crew coaches
Administrative vehicle (customs, etc.)
Maintenance vehicle

Services for departing flights

Mobile staircase
Coach busses
Baggage loading
Cargo loading
Catering
Refueling
APU
ASU
Pushback
Crew coaches
Administrative vehicle
Maintenance vehicle