Make a stand-alone weather data recorder to collect air pressure, air temperature, and humidity data using only an Arduino, SD card, LCD display, and solar power.
Provide a more tactile experience for your customers, who won't even need to physically visit stores while optimizing conventional production processes and eradicating the tenuous tasks that nobody really likes to do.
Learn to set up a Pi-based game development environment, and then develop a game with Lua, a popular scripting language used in major game frameworks like Unreal Engine (BioShock Infinite), CryEngine (Far Cry series), Diesel (Payday: The Heist), Silent Storm Engine (Heroes of Might and Magic V) and many others.
Now that you've built a few Arduino projects, and reused some pre-written sketches, it's time to move on to the next step and explore the world of embedded programming.