I've noticed that the Walnut, a nut very popular in France and Italy, two countries full of generally sociable and jovial people, is good for improving mood. It's apparently high in an amino acid called tryptophan. Your body needs tryptophan to make serotonin. Recent research suggests low serotonin levels leads to obesity, difficulty sleeping, depression, difficulty concentrating and migraines.
Some days I'll fry about 7 or 8 walnuts in some olive oil. Those days are usually the better ones in terms of how confident I am and upbeat.