Hey Ncc, welcome again.
Unfortunatley for your lead food, driving technique is the #1 mod to do to a car to improve mileage. Check out the
100+ ecodriving tips here and pick out a few and try them. I'd highly suggest looking at pulse and glide, driving without brakes for techniques. With a little work you should be over 40 mpg easily. As for immediate mods, pump up those tires to max sidewall pressure. The car will handle better, tires will last longer, and you'll get better mileage. The only downside is a slightly harsher ride. The grill mod will help the car warm up faster, but unless you do a lot of highway traveling, your not going to see the aerodynamic benefits from it.