One interesting way you can extend your Scratch projects is by connecting them to a Pico Board. These small, inexpensive circuit boards plug into your computer using a USB cable and allow Scratch to "talk to" a number of different sensors - sound, light, voltage, as well as a button and slider. This opens up some really interesting possibilities for your programs.
Here's a quick video overview of the sorts of things you could do with a Picoboard connected to Scratch.
You might notice that video was showing the older classic Scratch 1.4. The good news is that Picoboards DO in fact still work with the newer Scratch 2.0 once you set them up.
To set up your PicoBoards in 2.0 go to the More Blocks category and click Add an Extension. In the dialog box that appears doubleclick on the PicoBoard image. You'll be taken to the help panel where you can download the appropriate Plug-In for your operating system (Windows or Mac)
Download and install the plugin by following the instructions, then restart your browser and you should be ready to roll with some PicoBoard programming action! You can tell it's working when you plug in the PicoBoard hardware and the PicoBoard blocks in the More Blocks extension category have a green dot next to them.