I wish I had a track close by because I'd definitely do more interval training.
I like that the Marine Corps balances our tests. In the spring we run the PFT (3 mile run, pullups, situps) and in the fall we do the CFT (880m run in boots, 35lb ammo can presses, and a 2:45-5 min, dependent upon fitness and strength, maneuver under fire dill with sprints, buddy carries, ammo can carries, a grenade toss, and some low crawling).
The skinny dudes typically do pretty well on the PFT - Not too many 200lb + dudes running 3 miles in 18:00 to max the test or doing 23 strict pullups, but those little guys tend to struggle in the fall when those 200lb dudes carry those ammo cans and other people like they're nothing.
Bottom line, do a combination of dedicated strength based training, crossfit-like workouts, eat healthy and you'll be fine on pretty much anything.