This is a tough one.. I find it hard to concentrate on anything when I am feeling anxious. But I get the feeling that the use of "butterflies" means you are not at the anxiety stage. So some of the things I like to do are:

meditation
listen to my favorite songs
go on long walks in the woods
Paint
write
read

My T also gave me a cd of relaxation methods. One I found really helpful (sorry I forget the name) but when you tighten your muscles and relax them - starting at your feet and working your way up to your head until your whole body is relaxed. It's to teach your mind and body how to work together to relax and after a few times doing it all you have to do it think about your muscles relaxing and they do (without you having to tighten them first).

I guess the trick is to find things you like, but that requires concentration so that you are focusing on what you are doing rather than on what is giving you the butterflies.