I've had that pizza box for the longest time but never got down to using it because when you discover a pizza, you eat it up if the box is full anyway so that restores your energy.
But in the hope of better regulating the energy, I decided to eat up the Pizza that's been in the box for more than a month. That restored the energy to full and I get an extra mission out today.
Probably the most efficient in theory is to do a mission that drains 100%, recover to 40%, do a lesson which will bring you back down to 0 and then eat a pizza and do another 100% mission. Just a theory that I hope to try out.
The next thing to do for me is get a coffee cup so that I can restore energy faster after finishing a mission. They're going for only 5,000 Starbits but I'm saving up for my next pack so it will have to wait till I hit 10,000 starbits and then some.
Slowly, I hope to become a Starbit Millionaire too!