One of the things that work for street food in Asia than western food is no refrigeration. Sounds crazy right?
A litre of milk can last at room temperature for (only?) 6-8hrs, however it will last a week with refrigeration. So guess what happens in the west, we have some, put it back in the fridge and we could be actually having week old milk and be OK with it.
So in asia, (and include Singapore & HK as well as less development countries like LOS & Vietnam) the hawkers and street food vendors only buy the amount of food they will sell/serve that day. They can't store it for overnight. If they are out, they close up and go home. If they don't sell it, is thrown out or given away. But the food we have during the day is unbelievably fresh and what is in season.
Fresh, hot and in demand is the best rule if anyone who is worried about street food.