To be honest, since you have a solid DAT score and GPA, neither of these two things will really matter to admissions, or at least that was the case for me. I had the opportunity to do an honors thesis, but I didn't see the point and for me I felt it would have been a waste of time and unnecessary stress. If you really want to write one, go for it, but at least in my case and I'm sure in many others, it doesn't matter at all. Same goes for double majoring, if you have the time as it seems like you do and it's something that really interests you, go for it, it could only help. In the end, I think researching/volunteering is the best use of your time seeing as you don't seem to need help academically.