No food or water will be available after Tambaram, since the train passes Chengalpattu, Villupuram and Vriddhachalam Junctions at midnight. So have enough water and food.
But you can get Tea & Coffee at Vriddhachalam, only if you are in the front compartments of the train ,since most of the compartments will be standing at the far end in dark. You can walk till the front and get it as there is an ample time for loco reversal. In the morning at 5.30, pantry guys sell Tea & coffee.