You could probably hike more than 100 miles without food, if you had to. But hiking is supposed to be a fun adventure, not a have to experience. Keeping your engine fueled up with tasty, nutritious snacks while out on the trail for the day makes it much more enjoyable and easy.
The key thing to remember is to take something you like to eat. If it's chocolate, it might melt. If it's soft, it might squish. But, it will still taste good.
Here are a few choices for simple, convenient trail food.

Trail Mix

I have sitting in front of me a large bag of Kirkland Trail Mix from Costco. One ounce (28g) contains 150 calories. Of those 150 calories, 84 (or 56%) are Fat. Ouch! So much for the healthy trail mix fairy tale. It sure tastes good though, and some of it is just fine, but not handful after handful. You can see a Trail Mix recipe if you'd like to make some.

It's fine to consume more calories when you're in the outdoors burning off more calories than normal but you might as well make a bit of an effort to eat healthy food. One day of hiking and eating high-fat food probably won't hurt, but it also won't make the hike any more productive. Calories from simple sugars, complex carbohydrates, and fats are useful in different ways to your body. For ongoing energy boosts while hiking, the quickly metabolized carbohydrates should be preferred.

Here's a table of some foods, their approximate calories in 28g, and amount of carbohydrates, protein, and fat:

Food	Cal	Fat	Pro	Carb
banana	100	.5g	1g	24.7g
dried apple	68	.1g	.3g	18.5g
dried apricot	67	.2g	.9g	17.5g
raisins	84	.2g	.8g	22g
tuna	33	.2g	7.2g	0g
cracker	142	7g	2.2g	17.4g
cheddar	113	9.3g	7g	.4g
granola	137	6.8g	4.2g	14.9g
granola bar	137	6.7g	2.8g	17.7g
peanut butter	165	14.3g	7.2g	5.3g
peanuts	170	14g	7g	5g
jerky	116	7.3g	.4g	3.1g

Dried Fruit

On day hikes, carrying a couple apples or other fresh fruit probably won't tip the scale on your pack and they include important water that you'd need to carry anyway. On longer treks, drying your own fruit is a great way to reduce weight and still get healthy food.
Dried fruits are a great choice as long as you dry them yourself and drink plenty of water when you eat them. Drying yourself means they do not have extra chemicals and sugars added. Water is needed to digest them - if you don't drink it, you'll get dehydrated digesting the fruit.
Fruit contains good vitamins and calories with very little fat.

Tuna and Crackers

Grain is also a good source of carbohydrates. Breads and crackers are a good choice for day hikes.
Tuna fish contains high protein and is a good meal with cheese on crackers if you like the taste of tuna. Oh, don't get the tuna in a can - it comes in foil pouches now that mean much less weight and easy to pack. Don't forget a sturdy zip-loc bag for your trash, especially the smelly tuna pouch.
Have tuna fish recipes ready for your next hiking adventure.

Energy Bars

You can find these fancy treats in grocery stores or pay more for them at outdoors stores. They pack a lot of calories in a small, heavy bar but you may have to eat a few before finding one that you enjoy. I've gone through quite a few and most just don't taste that great to me. I do like the Lara Bars pretty well and some Clif Bar flavors are good.

Bar	Wgt	Cal	Fat	Pro	Carb
LUNA	48g	190	6g	9g	27g
Power	65g	240	3.5g	10g	45g
Clif	68g	250	2g	10g	51g
Lara	48g	190	9g	5g	24g
Peak	77g	300	6g	20g	48g

Jerky

Dried meat isn't a source of carbohydrates, but it is a nice treat on the trail. I really prefer home-made jerky since I can spice it just how I want and make sure its as dry and chewy as I want.
I can make a bit of jerky last a long time when trodding over not-so-exciting stretches of trail. Just like dried fruit, make sure you're taking in plenty of water along with it to keep things moving along on the inside.

Be sure to take enough hiking food with you on your outings and try to keep it healthy. After all, you're out there to enjoy nature and do good things for your body, so you might as well give it good food for fuel. Treats like trail mix are fine in moderation and drink lots of water!