I am a native of south India. The place where I come from follow a tradition of sitting on floor in an order and eating food on banana leaves (as plate), with hands. Sometimes we also form a separate order for ladies and gents, just to make ourselves sit comfortably. Once we are seated, the food is also served in a order. Starting with the cereals and vegetables, ending with yogurt.
Sitting on ground: The position in which we sit is called Sukhasana, a form of yogasana. This posture helps to calm the mind and applies pressure to the lower spine which helps in relaxation. So, we are actually performing yoga while having food.
Another reason being, we bend forward to eat and backwards to our main position. This front and back movement helps muscles in the abdomen to secrete digestive juices which in turn helps in digestion.
Eating food on Banana leaves: Practically banana leaf is large enough to hold entire meal. The leaves are also waterproof due to their waxy coating.
The coating is considered to increase the flavor of our food, making it taste better. Scientifically, surface of the banana leaf consists of polyphenols, a natural antioxidant, helping to prevent microbial infection and other benefits.
Eating with hands: One main reason we could think of is, hands act as an thermometer, we can actually verify the temperature of the food and prevent burning of tongue.
Some believe that hands act as energetic cleanser. The food is actually passed from the vendor to the chef and to us. So our hands are capable of cleansing all the negative energy present in food,thus preventing negativity from impacting our soul.