CloudReady supports the same suite of applications and peripherals as a typical Chromebook, including USB and SD card storage, headsets, microphones and webcams. For a full explanation of the components that are tested as part of certifying a CloudReady device, see our QA Checklist.
Not every CloudReady device has 100% functionality of all components. Neverware documents any failures or exceptions to specific features and functionality for each supported model - see our certified models list for a link to each device's notes. If you are using a non-certified model, there will be no way to anticipate issues.
Many other peripherals like CD/DVD drives, FireWire, docking stations, or anything else not listed here may function to varying degrees, but like with official Chromebooks there is no guarantee of support for these peripherals.