Abbreviations for the auto complete/intellisense feature.
I.e. create autocomplete suggestions based on a abbreviations - this can improve typing by a huge amount on big projects, especially when there are lots of names starting with the same letters.
F.i. if you have a lot of names like these
WINDOW_FLAG_CAPTION
WINODW_FLAG_SIZEABLE
WINDOW_FLAG_CLOSE_X
The typical autocomplete feature isn't that big an improvement because you have to type a lot before you get a good suggestion. But with the abbreviations you could write WFP, WFS, WFX instead which is much faster. In addition, this helps a lot if you search for a name, but don't know exactly what you're looking for, you just try a few abbreviations and see what the suggestions are.
This is a feature I got very used to while working in Visual Studio with the Visual Assist plugin, it's available in Sublime too.