Advice for caffeine-quitters: Quitting caffeine cold turkey is really hard on your mental and physical state and (from personal experience and research) the worst way to do it.
If you're a soda drinker, you're already cutting out high levels of sugar and caffeine, so start by cutting one out first by decreasing over a period of weeks, then cutting the other out in the same manner.
I get up at 3:45 a.m. Mon-Sat and work 10 1/2 hour days as a CNC machinist, plus I'm a single mom. So needless to say, caffeine is my friend. But I've recently started Adderall (Amphetamine) for ADHD and have also been having serious GI problems that aren't fully diagnosed yet, so I figured the caffeine had to go until I'm used to the new meds and also for my digestive health.
The best way to do it is to trick your body slowly and do so by switching to drinks with less caffeine, but enough to get you by. There are tons of things with caffeine, like hot tea that is steeped longer for less caffeine and even hot chocolate has caffeine (but less than coffee and sodas do).
I buy my favorite flavors of Starbucks and Green Mountain coffees, except I buy one bag of decaf and one bag of regular and mix it in the coffee maker each morning, adding less and less of the regular every few days. (That's to start off with in the morning, for example).
You can also cut down by alternating with water to rehydrate your body and make your brain/concentration better and make muscle soreness, lack of energy, etc. a bit less awful. Instead of five cups of coffee/soda at work, drink one cup of coffee, then a bottle of water, then a cup of coffee, then a bottle of water, etc. Drink the same amount of total "drinks" per day, but fill in half of what you'd normally drink in caffeine with water/juices/gatorade.
Best tip that people don't think of. Taking a multivitamin is always good for you, but I take the One-A-Day (I think that's the brand) multivitamins in the morn that are "Active Lifestyle" or "For Metabolism" because they contain smaller amounts of caffeine (about a cup or so) and also typically contain ginseng (a natural energy booster that doesn't have the "crash" effect and has other beneficial health benefits).
They're cheap, at every drugstore in many brands (including generic) and will help you get a kick of energy in the morning (plus improve your health while trying to kick your caffeine levels down).
You can also buy the flavored packets of things like Crystal Light (meant for bottled water) that contain caffeine and B Vitamins and try substituting a few bottles of water (with one packed per bottle) in place of sugary soda and strong coffee when you absolutely need a boost (but are still getting hydration and the benefits of physical and mental energy from water).
Even better is just buying Siberian Ginseng (Eleutherococcus Senticosus) capsules/supplements to replace your caffeine habits altogether. You'll not miss your caffeine one bit with these.
It's important to note that the difference between American ginseng (Quinquefolius) and Asian Ginseng (Panax)!
Siberian ginseng provides energy and stamina, maintains and improves mental alertness, boosts immunity (to colds, flus, etc), enhances vitality, and even helps build muscle strength/physical health. It is even found to help the body produce more T-Cells. More importantly, it acts as an "adaptogen". Adaptogens help the body to better deal with stress, both mental and physical and therefore can greatly improve moodiness and anxiety from caffeine withdrawal.
Studies have shown that after just four weeks of taking a (quality) Siberian ginseng supplement(s), mental health and social functioning improves.
Make sure you buy read up or hit a good vitamin store or "naturals" website to purchase these from. Make sure the product is at least 50 percent "pure" Siberian ginseng. Some cheaper blends contains as little as 20 percent of the ingredient and use low-quality content. This is definitely your best bet and they are cheap (about as cheap as buying good quality Vitamin E or a decent multivitamin) and can be found at drugstores, GNC and nutrition stores, and tons of online vitamin/herb shops. It's the best cure for caffeine withdraw that I've found/used.
For the mood-related element, you are irritable, depressed, cranky, etc., because caffeine stimulates dopamine in your brain that contributes to happiness, excitement, thrills, alertness, etc. Nasty moods are decreased by raising levels of dopamine, serotonin, norepinephrine, GABA, and Acetylcholene.
One example of a drugstore vitamin you can buy to naturally boost serotonin levels (and also melatonin levels) is 5-HTP (5-Hydroxy-Tryptophan) which converts to serotonin and then to melatonin (to regulate sleep cycles). It's an amino acid and they're great for boosting the "happy" levels in your brain without prescription drugs, caffeine or sugar.
You can buy the individual herbs/supplements you want to try (it's usually cheap for a small bottle of any type and are available in all stores that have a pharmacy/vitamin section) or you can try the more expensive blends if you're not familiar enough with supplements or just want to take one pill. An example is "MindPowerRX" (sounds totally cheesy, ugh) which can be bought online and in some nutrition stores. It contains many of the herbs/aminos/supplements that you could take alone, in combos, or in a complete supplement like MindPowerRx such as: Ashwagandha, bacopa, fo-ti, ginkgo biloba, ginseng (Siberian), gotu kola, mucuna pruriens, reishi, and rhodiola, acetyl-l-carnitine, carnitine, carnosine, choline, DMAE, inositol, methylcobalamin, pantothenic acid, trimethylglycine, and vinpocetine.
Most of these are easy to find/buy in most stores and are pretty cheap. You can also look for kavakava and valerian root for just the "calming/stress reducing" element, but they're mostly geared toward the "sleepy" kind of relaxed.
Don't forget that when desperate and having a caffeine-withdrawal headache, there's always Excedrin Migraine! You get the small amount of caffeine you need to avoid the withdrawals and the muscle/headache/inflammation relief you need as well!
This ended up being super-long, but I'm a huge fan of caffeine, as well as herbs, supplements, vitamins, teas, and things that can offer awesomeness without all the chemicals, side effects, and wear and tear on our bodies!
Good luck! You'll be on to better energy/mood products in no time!