All of the above, but wanted to emphasize something that goes with the granola bars mentioned.
Hydrate!
You'd be surprised how easy it is to "forget" to drink fluids while you wander around the floor. I usually bring two or three 16/20 oz bottles of water and make sure I pound one by noon and polish off the rest in the afternoon. You might be lugging around the weight of the water initially, but as that backpack gets heavier during the day, it will definitely give you the incentive to drink the water rather than carry it around.
