I just thought about sharing this, after reading TheCatWoman's post about having a Mammogram. For quite a while I wanted to have a colonoscopy, but it's not possible unless you have blood in your poo. But if you are 50+ you can get a test kit for bowel screening.
Well, I am 31 but I may call them to ask whether it is possible to have a bowel screening, since I've had some issues with my intestines. The link above is for England, I am reading for Scotland here.
I contacted them, if you are younger, you can ask them to your GP (they may issue it or not, but it is possible.)
Maybe others have comments, or other screenings they consider important.