You may have several attachments within a Gmail email thread, but it’s too time consuming to download one attachment at a time. There’s a Forward All option in the top nav menu that allows you to forward the thread back to yourself, thus allowing you to conveniently download all attachments in a gmail thread. See instructions and credit below:
Step 1: Open the email thread with attachments
Step 2: Click on the top menu and select “Forward All” and forward it to yourself
Step 3: Open the forwarded email and at the bottom, you should have an option to Download all
Credit to HansBKK: https://productforums.google.com/forum/#!topic/gmail/NPGn1YYgL8o