Chemistry is unique in sitting evenly between the other sciences, involving mathematical, high conceptual and practical activities, and to some extent, an artistic component as well. For example: Organic chemistry is essentially the chemistry of life, and topics as diverse as amino acids and reaction rates link well with Biology. Atomic structure is concerned with interactions between fundamental particles, entropy is the fundamental idea behind why anything ever happens at all, and these topics link well with Physics. Mathematics will help with calculations and working out units, but you will get enough training on this from the Chemistry department if you are not actually studying mathematics itself. Also, due to its development of analytical and problem solving skills, Chemistry would be a good subject to study in conjunction with subjects such as Psychology and Geography.
A qualification in Chemistry is highly valued and leads to a wide variety of careers, including the Prime Minister of the UK. If you are undecided, many options are kept open by studying Chemistry.