1. Four major mechanics, including classical mechanics, thermodynamics, electrodynamics and quantum mechanics. The order of study can be in the order I listed.
2. The basic requirements of mathematics are calculus and linear algebra. I think you should already have this foundation. A slightly advanced application requires basic variational methods and complex variable functions.
I will probably list the prerequisites for other advanced courses.
1. differential geometry->; Theory of relativity
2. atomic physics->; Elementary particles (nuclear physics)->; String theory
3. quantum mechanics+electrodynamics->; quantum field theory
Gravity field is something you will encounter in string theory and general relativity.