Generally, contractors such as Skychefs charge astronomical fees called "Door fees". What this means is... for every service entry they pull a truck onto, the Airline is charged the fee just for them being at that door. Some Aircraft have three or four doors and galleys. The supplies are ADDITIONAL charges, and they are marked-up several hundred percent above retail. It is for that reason outsourcing is not always a cost saving pursuit.
For the most part AA has eliminated the need for catering at most out stations by double catering in the hubs. I recently flew SMF-DFW in first class and the FA stated all she had was cereal and a bagel because that's all they send in the night before on the same plane. That's pretty sad on a 3.5 hour flight if you paid full fare for FC. At AA the outsource cleaners provide all the cups and coffee, napkins, sugar, etc.