Over the past couple of years, I've switched from using DADGAD tuning to Drop-D exclusively for session backup. It took some time and a lot of effort to make the transition, but I think it was well worth the work.
I'm a huge fan of John Doyle's playing style and chord progressions, highly recommend any of his workshops and instructional videos.
If you have a Drop-D backup tip you'd like added to the site, or just want to say hello, please send me an email!