My 2 normal breakfast's are:
bran flakes with soy milk and then a banana later on. This usually keeps me good until lunch since there's almost 10g of fiber between the 3 and about 10 of protein as well.
Or, which this keeps me full longer:
packet of flavored oatmeal, 1/4c regular oatmeal, 2T ground flax .5c soy milk with 1/4-1/2c water. This generally keeps me feeling nice and full for about 3-4hours and comes in around 400 calories with 13g fiber and roughly the same in protein.
But, some mornings we're just hungrier than usual. Sometimes your body just needs a little more. I find that if I wake up hungry in the morning then I need to eat a larger breakfast. Most mornings I don't wake up super hungry. Today, I woke up feeling hungry and I only had the cereal and banana later on. Now, I'm starving! So, sometimes it just depends on the day and also what our day before was like. Yesterday I worked out pretty hard and stayed around 1600calories, which is higher than my normal but because I did pretty much exhaust my body it was probably a little low.
Anyhow, I hope you make it to lunch time! I would recommend keeping some high protein and fiber options at work. I keep something like that in the car now just in case I'm out and need a quick bite to eat. It saves me from stopping and getting junky food that I'll regret later.
