Physics

I am not sure about physics, but surely you can combine maths with your humanities subject. If you have economics in your humanities subject then maths as an additional subject can definitely prove to be a boom for you. Knowledge of core mathematics is highly necessary for understanding the advance theorems of Marco-Micro economics. When it comes to the understanding the concept of consumers producer behaviours, price determination, revenue recognition, etc., you must have the knowledge of matrices, differentiation & integration, statistics and probability. These concepts help a lot while having an advanced and realistic knowledge of economics (as a part of humanities). So, in this way, we can relate the subjects of maths and economics. Here, physics may not help you much (since physics is the application of mathematics in the practical world), but it may help you to enhance your mathematical calculation skills. Hope this helps.
Best of luck.