One rule of thumb is that unless you're running for about 90 minutes straight, you're not going to use up your body's energy reserves, so you don't need to worry about "fueling" for a 5k training program. Just eat a good, balanced, healthy diet. If you normally feel hungry in the morning, then eat something before you go out if you want -- Something easy to stomach, like a piece of toast, or some oatmeal, or small bowl of cold cereal, etc.  If you don't really feel hungry (like me) when you get up, then there's no physical reason to eat first, assuming you didn't starve yourself the entire day before! Some people like a little coffee or juice too; some don't. Don't guzzle a bunch of water but be sure you are adequately hydrated (always -- not just before a workout or run).

I had the same problem for a while trying to figure out which foods to eat. First rule, avoid dairy/milk products. Maybe the night before but in moderation, definetly not in the morning as it takes much longer to digest and upsets your stomach. I suggest much water the night before to "flush" everything out, and maybe a light peice of toast and an apple. Carbs and fruits or veggies. Depends on how much you run. Usually I only go about 3/4miles. If your training harder then you might want to eat less or more, depending on how well your stomach handles food. And eat it at LEAST 30 minutes before you even start to warm up. Hope this has been of some help.

What you eat for an evening meal won't have a lot of impact on your morning jog.  Of course this is assuming you eat a sensible diet to begin with.  The only effect your evening meal might have is if you eat something extremely spicy, heavy or fatty which gives you indigestion.

You can experiment with what works best for you in the mornings but generally nothing at all or something easily digested is your best bet.  For me, personally, coffee is a must.  If I am running later in the morning, I eat oatmeal, whole wheat toast or a banana.  (I can't tolerate milk or eggs in my stomach when I'm running, but that's just me.)   Unless you are running for more than an hour, you can run before breakfast - or with a very light breakfast - and you'll do fine.