An interesting feature is integrated in the latest update to Gmail in Android, providing attach files from Drive. As we see in the picture, when drafting an email we see that it has integrated a new option when attaching files.
Just choose the option to integrate files from Drive, will have a display of our own to select the document you want to send.
We may also edit the permissions of the file before sending it, to send it as wish, without leaving the email interface. And as a bonus, have also improved autocomplete suggestions for contacts when sending email.
Small details that greatly simplify the process of sending emails from the phone or tablet, saving a few clicks, not entangled with too many options. All these new features will be gradually rolling out to all users.