Ctrl + Shift + T
Ever accidentally close a tab and actually still need it? I make that mistake daily. Ctrl + Shift + T is like a magic wand that returns the tab to my screen and smooths my knitted brow. You can use it to get back up to 10 tabs! Try it in Chrome or Firefox.
Ninja teacher tip: Use it when a student suspiciously closes a tab and looks around to see if anyone noticed.