Oatmeal bars make for a great snack. But it's better to make your own since the commercial ones are expensive and aren't all that healthy, and you can put whatever you want in them. There's a ton of recipes online but they are all pretty much the same. They aren't hard to make, and only take about 30 mins.
Just substitute some of the sugar for fruit combinations or nuts. Bananas, apples, strawberries, pears, blueberries, and raspberries are all good choices and crushed almonds add a whole lot of flavor while still being healthy. If you don't mind cheating a little on the healthy stuff, make a batch with something sweet like peanut butter and chocolate chips. Oatmeal is high in fiber, so it's healthy for you no matter what you put in it.
Don't get those little packets of oatmeal that come with dried fruit already inside that you just add water to make. These are loaded
with sugar. Steel-cut oatmeal is the most healthy out of the three types out there, but they take a very long time to bake and are usually expensive for a small batch. Plain old "Rolled oats" work best for bars, and you can get a giant tube of a generic/store brand for cheap.
Jell-O is another thing you can load up with different types of fruits for a healthy snack.
Some other stuff to think about is roasted seeds like sunflower or pumpkin (just be sure to get ones that are lightly or non salted).
You can make a few healthy versions of chips too. It's as easy as slicing them very thin, rubbing with olive oil, and popping them in a very hot oven for a few mins. Russet potatoes are great for potato chips, but stuff like sweet potatoes and beets are also great.
And if you're not allergic to peanut butter, it comes in handy when you get a sweet tooth craving. Just a spoonful or two does the trick to tone that hunger down. It's healthy for you too since it has protein and fiber. But it's also loaded with sugar, so don't get carried away.