1. Embedded System/Robotics with Major Projects
2. VHDL/VLSI with Major Projects
3. Advanced Embedded System with Major Projects
4. MATLAB

I would suggest you to go through the course "Signals and Systems" as one of the productive things to do in your vacation. Of course, you could also learn (or practice) computer programming in different languages. You could even learn Arduino-ing, FPGA, HDL and stuff like that.