How to stay awake when really sleepy?

I work first shift, so I get up at 4 a.m. every day. I usually go to bed around 8 or 8:30 p.m., so I normally get 7-8 hours of sleep. However, whenever I am at work I am super sleepy. I sit at a computer all day, so I don't get much movement to help me stay awake (I usually walk around during my breaks at least). I also listen to music with my earbuds while I work, and that doesn't seem to help me stay awake either. I'm on the verge a lot of falling asleep at my desk. It's a tough battle. Does anyone have any tips on how to stay awake (that doesn't require caffeine)?