The Hamburger icon is just not what it should be, so I went shopping for icons and brought back... a whole list of groceries for all the possible buttons on the header bar.
I hope this will inspire the discussion about what icon to choose for each. Icons roughly in the order of: OOUI then my preference. Colors are arbitrarily chosen by fontawesome.com.
Tl;dr: Some icons are good, some are confusing, some are missing for the header improvements. See some ideas below for these icons.
Left 1. Table of contents
In case it becomes a tab on the collapsible sidebar.
Left 2. Site navigation
Personal preference: Wikiglobe with arrow below
Left 3. Article tools / editing
Left 4. Bookmarks
Right 1. Alerts
Mentions, direct messages, reverts.
Right 2. Notifications
Thanks, badges. The current icon in Echo is a UTP socket? A tray.
Right 3. Watchlist
Right 4. User contributions
Add small user icon in bottom-right corner of history/list icon.
Right 5. Skin settings
Right 6. User menu
Note: Consider not displaying the user name. Showing the username is useful on shared computers and for sockpuppeteers. Hiding the username is good for making screenshots that have no privacy concerns.