What matters most is what you want to DO with your physics combo degree as to how the information will complement your physics degree. If you want to do materials science, condensed matter or AMO physics, you'll want more coursework in chemistry. If you want to do theoretical physics of some form, you'll probably want more math coursework.
If you're looking to impress graduate committees with a dual major, it's not, however, something that typically increases the standing of your application much, certainly not much more than anymore than a strong minor or coursework in a related field (and I typically would say this would bump your application only a 1/2 point or so out of 10 in a reader's score, which in the case of our school, was averaged in with scores about GRE's, GPA's, etc.).
Note: I originally planned to dual-major in chem/physics, but ran into trouble with conflicting lab-times... so I ended up doing physics with two very strong minors in chemistry and math... (typically skipping some of the intermediate courses, like Intermediate Analysis, in favor of just moving onto the harder courses). I think that combo worked well for me.