I recommend looking for a bunch of internships first and see what kind of skills or projects they might be advertising, or look at the professors webpage to see what their working on. Then you'll know what can buff yourself on and advertise to them as a perfect candidate. Cater to the roles of interest!
I think python, MATLAB, and C/C++ programming is a good idea :) it couldn't hurt you and you'll probably have classes covering some of this stuff too.
My earlier internships were on nanotechnology and semiconductor physics. It's very research oriented. I'm far from being an expert, but I saw lots of projects at my time on things like graphene or carbon nanotubes (CNTs), emerging solar cell material, III-V materials like gallium nitride (GaN), and microelectromechanical structures (MEMS). If your school has access to papers you could look some up on things like scholar.google.com and just read a few of them or even look up papers directly written by the professors you are considering. I think these topics are very hard to understand, but if any of them catches your fancy that might give you some direction on what you might want to try or learn more about.
I'm not sure if it was just me or I'll just say from my own perspective... it felt like there were few opportunities with SPICE simulations. Something that popped up more often for me that did involve some schematics was importing them into layout. This stuff helped me with my first jobs. I would look around for any kind of workshops on CircuitMaker (by Altium) or EAGLE. I'm not sure if there's a free version of Allegro, PADS, or Zuken, but I see these ones all the time too. Some topics that are interesting are like choosing stack-ups, choosing trace width such as for signal integrity or RF transmission lines, and power distribution network (PDN). Altium by the way has a lot of "white papers" on this stuff, and signalintegrityjournal.com has a lot of good stuff too.
I think some DIY projects especially using Arduino, Raspberry Pi, or if you can afford one of the Xilinx boards would be very good. Xilinx has a Xilinx University website and you might be able to access their workshops. I would work on 2-3 or DIY projects could be something like instrumentation say for instance I did something where we made a homemade breathalyzer and a friend of mine did their own "smart" glasses. I've done some other very basic things like making a speaker or maybe a car that follows a line. Other control related things could be like a Verilog project that you just synthesize- can look up stuff from a digital design class example project might be like Fibonacci sequence or some compression like RLE in Verilog. If you got access to the Xilinx stuff you could explore embedded C and try some stuff out with SPI or I2C commands.
