Most tables in books I have looked at say that one average human requires 2600 grams of food, 686 grams of oxygen ( O2) and 400 grams of water. They then produce 857 grams of CO2, 857 grams of water and 1972 grams of waste.
I was surprised to discover how hard it was to find similar statistics for plants. One reference I found said that 80 'dry' tons of algae yield 40 tons of methane and 160 tons of oxygen. They didn't say over what time period so I assume it is over a 1 day period since everything seems to be referenced to 24 hours. Another reference said that 10629 grams/person/day of plants required 3219 grams/day/person of CO2; 69 grams/day/person of nutrients and 110216 grams/day/person of water yielded 2240 grams/day/person of oxygen and 158685 grams/day/person of water. So, comparing what a human needs in oxygen as 686 grams, it looks like you need about 3 kilograms of 'plants'. This doesn't sound like a whole lot to me, and I think I may be misreading the references I'm using. Sorry for the uncertainty!