I love these stain removing pens. I keep one in my office and one in my laptop bag at all times. They come in very handy for removing stains after accidents while eating. I have had pretty good success getting ketchup, soda, wing sauce, and grease out of shirts with this Tide Pen.
I used to keep one in my car, but during the summer, I think the liquid dried up faster, so now I keep it in my laptop bag, which I usually have with me. The clothes I use are not dry-clean only, so if you use dry-clean only clothes, I don't know if this will work for you. Maybe try it on an area of your shirt that isn't visible to see how well it works first.
The way it works is that you press the pen tip down into the clothes, and it releases some of the stain removing liquid. Then you use the hard tip to rub the liquid in, removing the stain.
I definitely recommend getting a few of these!