Definatly go for the maths and sciences but make your third or fourth a humanity subject, English literature would be the ideal pick 100%. History would be good too but its not important. People think that to do law science subjects are not ideal but if you can get a good grade in them you are the best of the best, university's will look at people with those difficult science and math subjects as the brightest . The subjects that will make you a top aplicant for law is someone with diversity so a math a science and a humanity subject combo would be ideal. Out of the subjects you mentioned I'd pick maths chemistry and history ( although I really really suggest you pick english) . Some person replyed saying pick history English economics..no no no, only pick one of history and English if you can help it..those combinations are so limited.
Finally pick what your good at, if your not good at any humanity subject but are great at science and math maybe a STEM degree is the path for you instead of law. Conversely if your not good at science or maths don't feel like you absoluty have to pick them. For law the main thing is diversity.