Unfortunately, I have to have caffeine almost everyday. However, instead of coffee or diet coke I have found a healthier option! Basically every morning I drink a large glass of Crystal Light with caffeine (strawberry flavor). I get the caffeine I need plus I get closer to drinking the recommended amount of water per day!
Being Irish also I know exactly what your talking about....although I do switch the tea with decaf coffee sometimes.
Now, it is copious amounts of Iced tea with lemon. At 90*+ it is too hot to drink anything hot or with much caffeine.
Dunkin Donuts french vanilla iced coffee.... just literally can't live w'out it! Dunkin Donuts coffee.... lots of it! I also enjoy a frosty margarita on a hot summer day.