One thing to consider, as mentioned in other posts, is the food that you are eating or have easy access to. You can start making it easier for you to choose better "pick me up" foods when you start having lower energy levels. One of the best, for some people, is raw cacao nibs or raw chocolate products. These can be very fast acting and invigorating without having the same potential negative effects of coffee and other high caffeine sources. Because raw chocolate is not heated, the theobromine, which is related to caffiene, does not take on the same over-stimulating effects of coffee. Still, some people DO NOT respond well at all to raw cacao and raw chocolate products. This can be due to lack of quality, and improper fermentation of the cacao beans leaving it containing unwanted microbe levels. Either way, if you notice negatives from it, it is likely better to choose another food. For those who respond well to it, though, it can be a very empowering food.
One reason for this is that it contains SO MUCH magnesium. Magnesium, as suggested in this post, is a very empowering and productivity promoting mineral, which many people are deficient in. Because supplements range in quality and effectiveness, eating foods that contain high levels of magnesium is a great start. Cacao is a wonderful food for this purpose, as long as you respond well to it.
The effect that this can have on productivity is varied. Very likely, if you are deficient in magnesium, having foods like cacao can begin to increase concentration and feelings of contentment. As a result, creativity and resourcefullness can increase greatly.
While productivity is surely not ALL ABOUT THE FOOD, it is definitely a leverage point to use when you are feeling less productive and don't know what to do to change it. Foods and herbs can empower you to feel more able to handle tasks, which can motivate you to go farther and challenge yourself. For this, it is difficult to find another food more useful than raw cacao. They can be eaten by the handful easily as raw cacao nibs, which makes it a great trail mix additive or substitute.
Again, this might not be everyone's go-to food. The key is to consider the use of some of the most powerful foods available as tools for personal development and productivity. Find those which you respond well to.
Spirulina, Chlorella, and Blue Green Algea are also very useful foods for this. You can buy spirulina or chlorella tablets, which some call "nuts", as they are easy to eat like a crunchy, somewhat nutty, snack. While they do often leave a blue or green color on your teeth, they can be a very empowering food and often provide long-term energy. Blue Green Algea is often available as dried flakes, which you can add to water or smoothies or sprinkle on salads for an increase in minerals like magnesium and PEA, which is a chemical we naturally release more of when we are feeling in love. PEA is said to promote dopamine function, which can affect our level of contentment and sense of willpower. All of these qualities can increase our productivity potential.