Besides food, another thing that's good for keeping you alert is aromatherapy. There are two routes for this.
The easiest route, that's directed mostly at you, put a drop or two of appropriate oils for alerntess (rosemary, & peppermint are good for alertness) on the back of your hand. Occasionally waft your hand near your nose for a pick me up.
On a slightly more involved level, you can set up a more standard aromatherapy diffusor to release some into the room. You don't want something overpowering. Just enough so that people walking into the room might notice, but then forget about as they get used to the subtle scent. Oil burners are traditional, but you might not want something burning in the room, when you are distracted with the game.
It's pretty amazing how something as minor as that can change the atmosphere of a game. Again, you don't want something that diverts attention. I've played in games where someone's burned incense, and that was too much. You just want some subtle scents that help keep people alert.
If you enjoy this and finds it works well, you could even get more creative. For example, simply using lavendar can have people relax more during the game. During a game that is mostly character interaction, this might be appropriate.