Where do I find aux files in Overleaf?

Update for Overleaf version 2: the menu has changed.

If you need any additional files, you can find them in the compiler panel under "Logs and output files" and "other logs & files".

This post is valid only for Overleaf version 1 (I do not know if it is still used). For Overleaf v2, see the other answer.

As far as I know, the only way to get all the auxliary files is to select Project (if not already displayed) and then DOWNLOAD AS ZIP --> Input and Output Files.

In this way you can download a .zip with all your auxilary files.

Note that you have to use Input and Output Files, not Input Files Only, which is the default if you only click on DOWNLOAD AS ZIP.