One thing to keep in mind is that not everything sold in health food stores, or in the "healthy" section of the supermarket is really that good for you. Many energy bars and energy drinks, for example, are quite high in sugar. Sometimes it's called fructose or in some cases organic types of sugar, but if this is one of the first ingredients, you are still consuming a lot of sugar and calories.
When looking for healthy snacks, it's best to look for foods that are both organic and unsweetened. A good choice would be organic multigrain crackers with organic nut butter. Peanut butter is not the best kind of nut butter; almond, cashew or sunflower butter is healthier. Peanuts have become a disputed "health food" in recent years. Organic peanut butter is fine once in a while, but these other nut butters are made from nuts that have healthier fat content. Another good choice for a topping is tahini, made from sesame seeds. This is traditionally used in Middle Eastern foods, but it's a great topping for bread or crackers as well.
Fresh fruits and vegetables are always a healthy snack. Apples, carrots, celery, mangos, blueberries, kiwis and pomegranates are all great. These can also be made into juices, of course. Again, organic is best. However, sometimes you can find fresh, locally grown produce that is quite good and not sprayed with chemicals, yet is not certified organic. This is usually a good choice, as long as you know it's grown by people who don't use harmful chemicals.
Aside from fresh fruits, you can also choose organic dried fruits and nuts. These can be purchased individually or in trail mixes. As with other foods, there is a wide variety of quality when it comes to things like dried fruits and trail mixes. Once again, look for the unsweetened kind. Dried papaya, for instance, is often sweetened. Fruits are sweet enough naturally, so added sugar only gives you more calories and the many other potential problems associated with sugar.
One traditional snack food that is not usually considered healthy is popcorn. Popcorn can be a good snack food if it's popped naturally and is not topped with an artificial butter substitute (as with movie popcorn). Start with organic popcorn, pop it either using an air popper or a traditional popper or pan, using a healthy oil such as canola or sunflower. Top moderately with sea salt and, if you need the butter flavor, a small amount of organic butter or, better still, clarified butter. There are a few all-natural bagged popcorn products available, but the problem with these is that they add too much salt. At home you can go easy on the salt or even skip it entirely.
These are a few healthy snack food ideas. You can come up with more. Most types of foods can be healthy, or at least neutral, if they are natural and not overly sweetened or salted.