To be honest.... Just eat more.
Whatever your calorie intake, you should steer clear of sat fats and salt etc.
Most of the stuff suggested here has been good - vegetables, oils, nuts and whole grains are where it's at. Eating sugary stuff is not worth it... It burns out too quickly. Fats and carbohydrates are your friends, so look into stuff like pasta and brown bread etc. but also up your intake of stuff like olive oil... Look at mediterranean diets, they are full of oil, but are one of the healthiest cuisines out there.
Fruit is good, but note that is it sugars you're eating, so having just fruit for dessert won't supply you with a long term source of energy, but does give you vitamins.
Also, if you are running a lot, make sure you're getting enough protein... Chicken and lowfat meats are great, they are not too high in calories but don't give you nasty sat fats... Eggs are great too, and so is dairy. Full fat milk has quite a high protein count, and a high fat count, plus getting some liquid into you is a good thing, as well as giving you calcium.
I wouldn't worry too much about vitamin C or iron... If you are a man, you lose very little iron in comparison to a woman, who can lose a significant amount every month. This is easily replenished by eating red meats (lean steak is great!) anyway, so as long as you eat animal products, it should be ok (supposedly iron-rich vegetables such as spinnach contain iron, but we can't digest it, helpful!
).
On the note of calorie-full drinks... Well, it will probably be sugar. So good if you feel you need it, but not really an adequate way of supplying energy...
So I suppose, fats and carbs are good, with protein to support your running... Vegetables are great, mix them with everything.
Tho this is kind of about healthy eating, not about calories, sorry.
Oh and jacket potatoes have a higher GI than glucose itself.... i.e. they are bascially the equivalent of eating sugar cubes, the energy hits and goes in a flash. Generally, potatoes are baaaaaad.