Under Tools – Options – Environment – Document, there are the following options
Show Miscellaneous files in Solution Explorer
This option allows you to keep track of other files you’ve opened that are not a part of the project / solution. These files will be listed in Solution Explorer – so you can navigate to them easily
<n> items saved in the Miscellaneous Files project
This option keeps track of how many files to persist in the Miscellaneous Folder even if they are no longer open in an editor. For example, suppose I have 10 miscellaneous files opened, and I have this option set to 5. If I close all 10 files, the first 5 will still be shown in the Miscellaneous Files.
Happy Visual Studio’ing!