This would be what I would highly recommend.
1) Block heater! Your short trip is mostly just getting your car to warm up. If your not using EOC, your using tons of gas to warm it up. Replace this with a block heater on a 3hr warm up time and you'll not only have heat in the winter, but a car that isn't idling at 3000 rpm at the stop sign/light. This is very important for short trips IMO. It will even help in summer.
2) Grill block. Again, aids with warm up time and aerodynamics. It'll also help keep some of that block heater heat in the engine bay.
3) Keep refining driving technique. Take a look at
my fuel log. The first few months don't show incredible gains. It takes some time to figure this stuff out and learn how your car likes to operate.
4) Yep, you guessed it, some sort of instrumentation. If you can't swallow the scangauge price, try the MPGunio. Keep in mind the other functions of the scangauge (load, tps, etc) are incredibly useful. MPG is by far not the only thing you need.