You are right. Onam is the festival of Malayalees. Irrespective of caste and religion all Malayalees celebrate it as per their capacity. A good feast, mostly vegetarian, is a must. Generally the Onam day feast will be in one's own house. Most of the members of family join together to have a nice lunch. Banana, cut into pieces and boiled, is a favourate item for Onam. Pappat and banana chips also will be there. Vegetarian curries such as 'Kalan', 'Olan', etc. will also be served on the day. Some sweet item also will be there.
After feast certain entertainments will be organized suiting each category in the family. Children play in the ground with small rubber ball. Men may go for cards play, while women will have 'Thiruvathira kali'.
Thus the Onam days will be celebrated by all the malayalees.
Gold Member, SPK