Favorites on this site tend to include the lean-burn Hondas (96-00 HX trim and 91-95 VX), the Geo Metro and Honda CRX and Insight. Off-the-lot, a Prius is a great buy for a new car.
The Geo will set you back a lot less than a clean Honda. The Civic VX/HX are capable of getting gas mileage relatively close to that of a first-gen Insight if driven carefully but have the advantage of having back seats. Sounds like your cargo requirements are quite minimal and most any car should satisfy them.
I think a really awesome car to have would be a 2nd-gen CRX with a D16Y5 engine (Civic HX) and VX transmission (the tallest D series tranny) but making such a beast would be rather involved.
Tank|Trip Milestones: Toothless
[x] [x] 33mpg - 138% EPA
[ ] [x] 36mpg - 150% EPA
[ ] [x] 39mpg - 163% EPA
[ ] [x] 42mpg - 175% EPA
[ ] [x] 45mpg - 188% EPA
[ ] [x] 48mpg - 200% EPA
[ ] [ ] 51mpg - 213% EPA