My advice is select the field that you are passionate about. Then, based on recent research, find out what specialty knowledge is of possible value. For example, an Inorganic chemist may need some course work (or more, a degree) in Engineering (or Material Science or math specialty) to contribute to nano technology (don't trust this list, talk to experts in the particular field). For, Organic chemist: Algebraic Group Theory or Computer Simulations techniques or perhaps Biology? The pairings can be very unexpected.
On the surface, this makes you a stronger candidate to get a job. Don't make a salary demand (say Open, you may even get more than you wanted!)
On the downside, don't be surprised if your co-workers will not be completely embraced you. For example, business majors and Financial Engineers work together, but the MBAs, in my opinion based on a very small sample, don't always trust or understand the quants, and the quants may even think even less of the MBAs!
Good luck.