If the area isn't too hilly, that distance is perfect for some roller blading.
On select days (sufficient light, no reason to avoid bike going to work), I head to work (6mi) by bike, and back again, then at home get out of the bike stuff, into my volleyball gear, put on the blades, roll the 1.5 mi (including a reasonably steep bridge) to practice, hang around for some 90 minutes, and back on the blades.
Hardest part is hitting the shower once at home, because by then I'm tired, exhausted and hungry....
Anyway, core strength + medium distance endurance is probably the most healthy excercise, so I'd recommend putting in at least 66% of those two, and spend the rest of your time doing whatever else you consider useful - unless you're training for competitions, in which case you'll have to be more dynamic about what to exercise.