In Jainism, Trayodashi refers to the thirteenth day of the lunar fortnight in the Jain calendar. On religious occasions such as Trayodashi, especially when observed as a fasting day (vrat) or as part of Paryushana or other auspicious periods, Jains follow strict dietary rules.

Typically, the food served (if any, since many may observe fasting or eat only once) will adhere to the following principles:

• Strict vegetarianism: No meat, fish, eggs, or root vegetables (like potatoes, onions, garlic) are consumed.
• No green vegetables: On certain Trayodashi days, especially during the Chaturmas period, some Jains avoid eating green leafy vegetables due to increased micro-organism activity during the monsoon.
• Simple preparations: Food is prepared simply, often without onions, garlic, or overly spicy ingredients.
• No food after sunset: Jains do not eat after sunset as a practice of Ahimsa (non-violence) to avoid harming microorganisms that are more prevalent at night.
• No fermented foods: Foods prepared with yeast or fermentation are avoided.
• Limited ingredients: During specific vrats or fasts, the number of food items or types may be further restricted.

Common foods (if eaten) might include:

• Boiled or steamed grains (like rice, wheat, millets)
• Lentils and pulses (except during certain fasts)
• Fruits and dried fruits
• Dairy products (like milk, curd, ghee, buttermilk)
• Sweets made from permitted ingredients (like milk sweets)
• Cooked vegetables (allowed types only)

Many devout Jains on Trayodashi, however, may observe upvas (complete fasting) or ekasanu (eating one meal in a day), and some may take only boiled water, that too filtered and during daylight hours.

The specific menu will vary by community, tradition, and the particular type of vow (vrat) being observed.

If you have a specific Jain sect or regional tradition in mind, please specify for more detailed information.