Type 1 Going to theme park

Hi fellow diabetics. I am going to a theme park next week with my sister and have found out that you can get a wristband so you do not have to queue for rides. This will be handy as my feet suffer quite badly when I stand for long periods of time (as fellow diabetics may know). I found that to get a letter from my doctor is £30. Does anybody know any other form of proof that I can use? Many thanks fellow peeps.