There are two parts to your question, so I will address them separately first, then in synthesis.

Stress reduction

Stress is simultaneously remarkably simple and terribly complicated -- simple to manage, terribly complicated to really understand. As for managing stress...

The first key is to recognize when you are reaching your personal stress limit. Don't wait to get there, be ready to take a break before you're "stressed out". The second key is to find a particular thing that de-stresses you; it's different for everybody, but with only a few exceptions there is a common thread -- ritual.

Habits or rituals are how most people de-stress. Personally, I get up and stretch, refill my glass of water, and go for a short walk (this is at work, FWIW). Nothing is magical about any of those activities (though physical activity tends to be a de-stresser of itself for most people), it's the ritual of doing so. I don't have to think for a few minutes, and that calms me.

At home, I've a different ritual: meditation. However, meditation is a skill, not something you can "just start doing" with positive effect, so it's not for everyone. Some people acheive the same effect with playing a few rounds of Soul Caliber. ;-)

The important thing is that you find some non-stressful activity that you can develop a habit of doing when you find yourself stressed. And remember, habits take several days (some say as much as 10) of contiual work to form.

Energy restoration/maintenance

There is one simple "don't" here: DO NOT rely on stimulants for regular energy boosts. Caffeine is a stimulant, so are sugar and the active ingredients in "energy drinks". I'm not saying you can never drink coffee or have an energy drink: just don't regularly do so for the purpose of giving you a boost. Stimulants aren't good for you outside of moderate doses, and if used regularly, a moderate dose won't have the desired effect anyway. Once you build the tolerance you'll either stop and go through withdrawal or start consuming higher, unsafe doses.

A good diet is the best way to maintain energy. What "good diet" means to you is highly individual -- hire a nutritionist to build a plan for you, it's worth it. And, the energy you have will be consistent rather than a high you have to crash from.

Adrenaline-producing activities are useful for boosting your energy as well. I'm an overweight geek, so I'm not a "my body is my temple, and I will run 3 miles today" kind of guy. But, going for a couple-mile bicycle ride only takes a few minutes and wakes me up when I need an extra energy boost.

And, though it may seem odd, my meditation regimen helps me here too. Meditation isn't a replacement for sleep, but with training one can learn to take "waking naps" that can carry you an extra hour or three on that demanding script you're working on. Also, the relaxation benefits of meditating in the morning and before lunch help keep me alert.

Synthesis (Understanding Stress and Energy)

Stress and energy are directly related: stress consumes your energy. When you're solving a difficult problem, notice how different muscle groups become tense (for me, it's my shoulders, neck, and jaw). You expend energy to maintain that tension, oddly enough, so relaxing and allowing it to release can keep you from wearing yourself out.

Going for a brisk walk might help you reduce your stress, and will also cause your body to process stored energy (fat, protein, and carbohyrates) and produce adrenaline. So, it wakes you up a bit (adrenaline), provides you with sustainable energy (metabolising), and helps keep you from using your energy too quickly (destressing).

Playing video games does this for my co-workers (sans the metabolic benefits), walking or meditating does this for me, and a tiny snack (a handful of popcorn, even) does it for my wife.

The imporant thing is to find some pattern, habit, or ritual that supplies you with energy (safely) and reduces your stress at the same time. Everyone has their own triggers, so you have to become observant of your own stress-levels and responses.

As silly as it might seem, keep a log of what you do and how stressed you feel, and what the physical symptoms of that stress are. If you go for a walk and feel more relaxed, jot it down. Do this for a month or two, and you should get a good idea of what things stress and destress you. Try to eliminate stressful things (not always possible, but I bet you could find one or two), and form habits that destress you. Forming the habit adds to the destressing quality of your chosen activity.

I keep mentioning meditation, because that's what works for me. The principles might be available to you in other forms, though. I have friends who have meditative experiences by listening to music (that's actually very common), and get the same benefits as I get from more formal meditation. Again, experiment to learn what works for you and get in the habit of doing it.