This is the simplest and most basic.
6 - hours of sleep a night
2 - good nutritious meals a day
1 - shower/bath
Sleep - Cons are busy active places and you don't want to missing anything, but if you don't choose when you'll miss something, you body will choose for you. Worse yet, you'll be so sleep fogged by the end, you don't remember any of it.
Meals - DO NOT graze the parties or consuite for your meals. They mainly provide sweets and carbs, not nutrition. Have a pair of well rounded meals, that provide all the necessary food groups. Besides, meals with friends is more fun then grazing.
Shower/Bath - You may think you didn't sweat, while sitting in those panels all day, but person sitting next to you thinks you did. Think how good it feels to end/start the day feeling clean and refreshed.
Note: Do NOT invert the food and sleep rules. Worldcon is 5 days long, you need your sleep and nothing can replace it.
Note2: My guides are basic starting points. Each individual is a individual (yet I meant that repetition) and should adust for themselves. However, I have found the above to be good starting points. Try them, then adjust them to suit yourself.