This page lists the essential data you receive with every bug report, out of the box.
You will find Essentials listed on the right side of your web Dashboard, and these include data like user's OS, location, memory status, etc.
Customizing the data you receive
If you want the SDK to attach any other variable to your bug reports, you can absolutely do that as well! Read about sending custom data with Metadata.
Do you also want to attach custom files, like images? Visit Attachments.