About 9 days each year, some Thai people would be observing a vegetarian diet. This is for the Nine Emperor Gods Festival which is also observed and celebrated in Malaysia and Singapore.
In year 2020, the date occurs from 17 October to 25 October.
During this period, you can find vegetarian food in abundance all over Thailand. For vegetarians who are staying in Thailand, it would be a good time to stock up as some of the dried food can be kept between few months to about a year.
In 7 Eleven, during this duration most stores would have a dedicated section where vegetarian food such as instant noddles (vegetarian flavour), curry paste and mock meat are being placed on sale:

Do note that the cup noodle Mama brand does not produce vegetarian flavour cup noddle. The only exception is during the Thai Vegetarian festival where limited amount are being produced. The cup noodle is actually quite delicious. Aside from that, there are vegetarian flavour instant noodles, which is available starting from few weeks before the festival.

They also have instant food and vegetarian flavouring that can be used for cooking vegetarian dishes.

Above are vegetarian chicken with chili paste.
If you intend to buy supplies to cook vegetarian dish or you are cooking vegetarian dishes for a lot of people, then during this period, you can source for your vegetarian food supplies from places like Makro. You can find a lot of mushrooms (dried or wet ones), dried soy foods, mock meat and flavouring.


Items are quite reasonably priced. But the main thing is, I really do not recall seeing varieties of these items available during normal time of the year. This is because during normal times of the year, the demand is not there. Personally, I do not recall knowing any Thai persons who are full time vegetarians. If there are any vegetarians that I’ve met in Thailand, they are usually foreigners.

Below are vegan red curry paste. Based on the label, the paste is produced early September and has a shelf life of one year (meaning it only expires in September next year).

There are sections in Makro that are dedicated just on vegetarian items:

Personally for me, I have observed vegetarian diet during the Nine Emperor Gods festival for more than 10 years while I was in Malaysia. I also used to observe vegetarian diet on the new and full moon based on the Chinese lunar calendar month. It was much easier for me to find cooked vegetarian dishes as well as vegetarian food supplies compared to Thailand that was why I literally had no problems observing it for many years because we would know where to get food or supplies.
It is a little different in Thailand where it is hard to find any vegetarian restaurant because the demand is not there. Only during the Thai Vegetarian Festival you can find lots of vegetarian food. Sometimes even food stalls that sell meat dishes would switch to sell only vegetarian food for that 9 days.
For a vegetarian, at other times of the year it would be self cooking- ie buying vegetables, tofu, mushrooms, etc and cooking them. Need to be careful to use the soya sauce instead of the fish sauce and to add salt/sugar for taste. Then there is the non meat sources of food. I’ve recently discovered frozen food like hash browns, roti pranta, mantao and garlic naans that are available in Makro. Yes, they are processed food but one can buy and keep. When hungry, these food would take only a short while to prepare.