If you are planning to attend graduate school in physics, a minor in mathematics would be beneficial. A solid background in mathematics is a door-opener for advanced degrees in physics.
On the other hand, if you are planning to seek employment right after a bachelor’s degree of science in physics, a minor in business administration (management, finance, etc.) or computer science would be helpful.
We should be mindful that there are probably not too many employment opportunities directly in physics for a holder of a bachelor’s degree of science in physics. Job opportunities will be concentrated in applied science and engineering areas, in which business management skill or computer programming skill, especially scientific programming skill, can add value to your basic science skill in physics.