you need to determine first what will fit into your overall nutrition plan. You are looking for an in-between meal, it seems, and that can be a lot of things, a nutrition bar being one option.
Among the nutrition bars, you have those that are more on the carbohydrate side versus protein. Some are nothing more than a glorified candy bar.
If you look at you overall eating habits, you may also assess your intake of fruits and vegetables. Many people fall short there, and an apple will make a great snack as well. If you add peanut butter (which is one of my personal favorites), you have added some protein as well. It is not as convenient as a ‘nutrition’ bar, though.
Wish you happy snacking.