I wouldn't trust anything the ward staff try and give you unless you have checked with your team first.
At Homerton the ward team tried to give me a full dinner just a couple of hours of surgery and then offered me a meal every mealtime the next day. They then failed to give me 'allowed' fluids apart from water until the day I left, even though the surgical team kept telling me i needed to get these other products (yoghurt, soup) in.
Be on the safe side and check with your team.
I try and stick with decaf tea and have done for a couple of years now, even pre op, because I have a heart problem. Caffine is also in things like chocolate so if i have a little i don't feel like i'm overloading on caffine.