What are some healthy snacks?

I eat breakfast, but a few hours later I am hungry again. Sometimes my solution is coffee, but I really would like to eat something that's easy to take to work. Fruits are okay, but sometimes if they are cut up, they turn brown which looks unappetizing. Fruits also--you never know if they are going to taste good or unripe when you buy them. I have taken mixed nuts and fruits, juices. What else do I take that's a good and healthy snack?