In Things Fall Apart, customs and traditions are a very important part of the Ibo culture. One such custom involves breaking and eating the kola nut. The most distinguished person at a meeting would break the kola nut:
In the Ibo culture, the kola nut is broken by the most celebrated person at an event.
The kola nut itself is filled with caffeine:
Kola nut, which contains high amounts of caffeine, helps combat fatigue and is most commonly used as a central nervous system stimulant that focuses on the cerebrospinal centers. It also contains theobromine, a stimulant found in chocolate as well as in green tea.
Offering kola nut at a meeting would be equivalent of being hospitable. If someone visited one, as a means of being hospitable, one would offer them coffee, tea, or soda. In Okonkwo's culture, showing hospitality meant offering kola nut and palm wine. Having good manners is showing one's guest hospitality. It is a necessary part of Okonkwo's respectful cultural traditions.
Also, no doubt the kola nut was used as a stimulant since is has caffeine. It would be used the way one uses coca cola. In fact, coca cola has properties of kola nuts:
Most people around the world are familiar with kola; many have tasted it and do not even know it. In the 1800s, a pharmacist in Georgia took extracts of kola, sugar and coca and mixed them with carbonated water. His accountant tasted it and called it "Coca Cola." Today, Coca-Cola still uses kola in its original recipe.
Most importantly, when entertaining, it is necessary to show good manners. It is a sign of respect. The proper custom is to show hospitality to a guest. In Okonkwo's culture, offering kola nuts and palm wine is the same as showing good manners and respect for the guest or guests.