Support ^W shortcut out of the box

{ "keys": ["ctrl+w"], "command": "expand_selection", "args": {"to": "word"} }

Seconding the DIY approach. Ctrl+W already has a common idiomatic assignment on Windows, "close tab or current document".

ST2 uses Ctrl+D to perform "expand selection to word", and also has the very nice additional effect of selecting additional matching words in the document when you press Ctrl+D repeatedly.