Before I gave birth to my second one, I only had one helper and I did all the food shopping and she share our food most of the time. At that time I also gave her HKD500 for "household money" for her to buy food she wants to eat and I will replenish it with the "expense report". I normally only have to replenish every 3 months.
After I gave birth to my second one, I hired an extra help. I asked them what they want for the food arrangement.( I still get rice, oil, noodles, coffee...etc) And they told me they would like to cook their own food, so I gave them HKD1,000 and replenish it when they give me the "expense report". In average, I have to replenish every 4 weeks. I'm a stay home mum, so I know clearly what they eat, and it is nothing expensive.(most of the time they have the same dish for two days)
The point I want to make here is HKD300 is really not enough for an adult to buy food in HK if they aren't allow to use the oil, rice, noodle...etc. espically with the increases in food price.