If you're already in science (which the OP is), a minor in another science is kinda pointless (ie. major: Chem Bio, minor: biochem)
But if you were to minor in something else (ie. major: Chem Bio, minor: Economics), then that will set you apart from other people and you can prove that you're a well rounded person who can do more than just science.
Info on biochem minor found here:
http://registrar.mcmaster.ca /CALEN...13/pg1518.html