Great post so yeah pizza slice can only be used once in a 24 hours. In terms of stacking im sure i am right in saying you only need one of each of the boosts. So 1 coffee cup that can refill,one pizza box that can store 4 pizza slices (im not sure if you can stack this further research needed) one slice of pizza that can be used once in 24 hours (again not sure if this one is stackable) and 1 risky whiskey boost. I think if you get one each of the energy boosts i think that would be enough for you to complete a good number of missions