Banana

Bananas are a nutritious fruit (or vegetable, as it is technically labelled as such under botanical terms) that is grown around Central America, including Costa Rica.

History
Around the 15th and 16th centuries, plantations were developed to cultivate Bananas. Eventually, the banana plantations stopped planting varieties of bananas and decided to plant the same sprout. This made work easier, but made the crops more susceptible to foreign diseases. Exports of bananas also resulted in an economic boom in Costa Rica, which gave them enough money to finish a rail stop.

During the events of the Peace Walker incident, the Militaires Sans Frontieres procured Banana Cultivation Instructions for cultivating Bananas at Mother Base. This allowed the Militaires Sans Frontieres to grow Bananas to, other than feed their troops, also use them as fake guns to hold up enemy personnel. Also, while attempting to recover a captive researcher who wanted to defect to the MSF, the researcher disguised himself as one of the scouts in Selva de la Leche's hillside, although he used a banana instead of an M16A1.

In-game description
"A delicious fruit (in botanical terms, technically a vegetable) from the plantations of Costa Rica. Low in calories and high in vitamins, minerals, and dietary fiber, it is an excellent source of nutrition. Many people know the banana chiefly as a snack or dessert or as an ingredient in baked goods, but in some countries and regions it is a staple food. Its shape vaguely resembles that of a gun. With a bit of skill, you could even use it to hold someone up...maybe."

- Banana description from Metal Gear Solid: Peace Walker