I'm interested in making a Google Inbox bundle that automatically grabs all messages with a certain type of attachment (eg. all MP3 files sent to me). I believe that Gmail rules had a way for this to be done, but does Google inbox have a way of doing this with their bundle feature?
It turns out that the answer is yes, this is already possible.
Though the placeholder text implies that you can only do a text match, it turns out that usual search filters actually do function in that box. So, you just need to select Includes and give it the value
has:attachment. In my specific example, also adding the text
filename:mp3 to the query allowed me to filter the attachments down to only MP3 attachments.