As far as I'm aware, both the sugar and the caffeine would send your blood glucose up. I'm fairly newly diagnosed too, but I think it's not usual to make a diagnosis until after two consecutive fasting blood glucose tests showing a level higher than 7. Someone more expert will confirm that or shout at me!
Your doctor also ought to ask for an HbA1c blood test which shows an average of your blood glucose levels over 3 months. I think 'normal' for this should be under 6 - again, others know better than me.
Have a browse round the forums (fora!) on here - you'll pick up some good info.
I normally have my fasting blood tests in the morning, usually after 12 hours with nothing but water. Fasting all day might affect your alertness and general functioning.
Good to chuck all the cakes, coke, sandwiches etc. All carbohydrates are metabolised into glucose so it all sends your blood glucose up. The monitors will send you some very useful information for newly-diagnosed diabetics, which is certainly worth reading even if you turn out not to be diabetic at the moment. If you're not, aim for a lifestyle that means, with any luck, you never will be - at least, not a Type 2.
Tell your doctor or nurse you want some proper information, and that you want to be pro-active in your treatment. And best of luck!
Vivienne