when they need to be replaced also go with skinny tire.
Remove the spare, most insurance companies have free road side assistance.
Get a vacuum gauge (usually also paired with a boost but you don't care about that) and when driving try to keep the vacuum as high as possible = better MPG.
You could get extreme and look at shaving your antenna on the roof and smooth that out. Perhaps see what you can do to tuck in the side mirrors. if skilled with body work you can install covers over the rear wheels to keep the body lines spokes on rims cause air turbulence can also look at new light weight rims that a solid faced (ford even has "convertible" rims on their new F-150 concept)
2001 ZX3 2.0L Zetec-
Hatch Nation #42
Going through Rebuild See "The TICK Build Thread" for details (http://www.focusfanatics.com/forum/showthread.php?t=289168&referrerid=62897)