It would save a lot of time, but it cannot be done.
It's one file to a container field.
You can set up a related table of records with a container field to store multiple files--each in their own container field, but your drag and drop of a group still cannot be done.
You may want to set up a folder on your desktop for this purpose, drag and drop your group of files into that folder, then use Import Records with the Folder option to import your group of folders. This only works with image or text files, however. If you are inserting/importing files of other types, you'd need to use a script that inserts the files one at a time. This can be done with a looping script once you have a list of filenames inside fileMaker to use for the inserts. This is possible if your folder is located inside the documents folder, or if you use a plug in to list the files in a designated folder or if you use a system script to create thelist of files in a folder.
Also drag and drop embeds the file--stores a physical copy of it--in the container field. This is often not the best way to insert files into FileMaker databases due to the way this can make for very large database files.
Thank you very much for the answer. I was afraid this was the answer and I was hoping there was something I missed.