I use #tags either in the subject or body of the email to enable pre-defined filters to apply appropriate labels on them to manage my common email workflows:
- Bookmarking: I email bookmarks to myself especially from my android phone (using the very convenient "Share page" via Gmail option) with the #bookmark tag.
- Read Later: This is an extension of bookmarking and I use the #readlater tag.
- File Storage: I email files or forward emails with attachments of interest to myself with the #files tag.
- Capturing ideas: I email ideas/notes to myself with the #ideas tag.
- Task Management: I haven't fully explored this yet.