Pre-workout snack?

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What's the best snack for quick fuel? I eat lunch around 12:30, and by the time I'm home and ready to exercise it's between 4:30 and 6:30. Especially when it's later, I need some sort of snack, but even if it's earlier I'm hungry and feel like I'm not exercising to my full potential if I don't eat.

I'm a beginning runner, and last week I did my longest run about 3 hours after a carb-filled dinner and was astonished by the energy I had. The next time I ran, I felt like I was struggling hard compared to that. I've been eating a piece of fruit or a cheese stick, but that doesn't seem to cut it. What do you like to eat before cardio?