[brucepick]

Injector kill switch.
This enables quick and frequent coasting with engine off.
Just a few $$ for a switch and some wire.

You'll need a dash mounted switch, but it's still stealthy when looking at the outside of the car. There's a thread (in DIY??) on mounting the switch on the gearshift, that thread was on a Civic. Mine is on the dash.

MPGuino for near-instant mpg data, updates 2x per second.
Or maybe a ScanGauge instead. But first make sure it will work with Elantra. My ScanGauge 2 does NOT work on my son's Elantra, don't know why.