ruby-string-interpolation package
Type # within a double quoted string to insert #{} or wrap the selection in it.
How it works (aside from cursor movements, the only key I press is #):
Changelog
0.1.5 Merged PR #2, this stops it triggering if you're in the Find focus
0.1.4 Had manually updated to v0.1.3 and then found out I needed to apm publish, which does it for you
0.1.3 Fixed bug where it had stopped working entirely