Her attempts to bring reusable containers for a takeaway at a fast-food restaurant get short shrift from the staff. 'If you want congee, they don't seem to be able to work out how much to give you,' Chan says. 'And some choices are pre-packed in throwaway lunchboxes.'

The environmental group Green Sense recently got a fair indication of how much we throw out at meal times after monitoring 90 outlets of five major fast-food chains: Cafe de Coral, Fairwood, Maxim, McDonald's and Kentucky Fried Chicken. The two-month study found that more than 2.7 million sets of disposable cutlery - plastic knives, forks and spoons - are issued to customers every month during lunch hour alone. What's worse, many may not be used at all.

Then there are the millions of polystyrene containers for takeaway orders. All will end up in the city's already overtaxed landfills, which are expected to reach capacity in as little as five years unless we curb our throwaway lifestyle. To minimise waste, Green Sense calls on fast-food restaurants to set up stations where customers can pick up the implements they need and reduce their use of throwaway products.

We buy, consume and throw out millions of tonnes of material without a thought to the consequences. They have a huge impact on the environment, not just in terms of landfill space and carbon emissions but also the energy, water and raw materials that go into their production as well as the amount of pollution generated. But what's best for the planet may not be as clear-cut a choice as you might think.

Consider your purchase of soy milk. At first glance, a paper carton seems more eco-friendly. But environmentalists say that's not entirely true. The paper is usually coated with thin layers of other materials - typically aluminium and plastic - to waterproof the container and preserve the liquid. So the carton can't be recycled effectively unless the different materials can be separated, says Michelle Au Wing-tsz, the environment affairs officer for Friends of the Earth. (Most recycling schemes are only able to extract the paper component, but Brazil last year launched a plant in Sao Paolo that can separate paper, aluminium and plastic using an innovative plasma technology.)

Glass bottles can be reused, but they aren't widely available and recycling the material requires more energy than plastic. At the same time, petrol-based products such as polystyrene are difficult to dispose of: incineration releases harmful compounds including cancer-causing dioxins, and they remain in landfills for centuries (according to US scientists, a polystyrene container buried in the ground today will still be there 500 years later). Some plastics also release chemicals as they deteriorate that may interfere with hormone function in humans and animals.

With soft drinks, Au says Chan is right to opt for aluminium cans as the higher profits they bring means there's a greater degree of recycling. 'Even if it doesn't end up in a recycling facility straight away, someone will pick it up for resale.'

Large retail chains are among the first to be affected by a proposed 50 cent charge on each plastic bag to curb their use (about 992 tonnes of plastic bags end up the city's landfills each year, forming the bulk of packaging waste). Under the proposal, all plastic bags will be taxed, regardless of whether they are biodegradable. However, paper bags are exempt for now as these will be dealt with under new legislation to be introduced in 2008.

So what kind of carrier bags should we have at supermarkets: biodegradable paper instead of plastic? While paper appears to be a 'natural' choice, the bags actually require greater energy input (2,500 British thermal units [BTU] are needed to produce one paper bag compared to 600 BTU for plastic). On the other hand, paper is more likely to be recycled and is biodegradable, while plastic is derived from non-renewable oil supplies and will continue to clog landfills. So what's the answer? Neither, green groups say. Both are bad for the environment, and a reusable cloth bag is best.

Although major supermarkets have signed up for schemes to reduce the use of plastic bags, activists say such action addresses only a tiny aspect of the problem of excessive waste. The rise of the mega supermarket culture has also made it almost impossible for consumers to reduce packaging waste, Au says.

'Think about it; many people don't buy from wet markets anymore,' she says. 'They go to the super stores where meat and vegetables are packed in polystyrene trays and plastic wrap. It's quick, convenient - and terribly wasteful.'

One way ahead is to switch to biodegradable packaging made from renewable sources such as cellulose from crop plants. About 15 Hong Kong firms use bags made of Enbio Mat, a corn starch-based material which can be 95 per cent broken down within 45 days compared to centuries for conventional plastics. They can cost twice or three times as much as conventional plastic. The usual plastic supermarket bag costs about 20 cents while a similar Enbio Mat bag costs between 50 and 60 cents.

Meanwhile, some food outlets are trying out biodegradable tableware despite the increased expense. ThreeSixty, a organic food retailer in the Landmark, Wonderfood Cafe in Telford Plaza and selected Cafe de Coral outlets will use packaging, takeaway containers and dinnerware made from renewable fibres such as sugar cane.

Packaging suppliers such as Growth Pack are betting on increasing demand for bio-based packaging. Although it used to make plastic packaging, it switched to distributing biodegradable materials following inquiries from health-food retailers and schools, says Growth Pack spokesman Otis Hui Sai-yim.

Idy Wong Lai-yin, the head of sustainable living at Kadoorie Farm, says the government can play a more active role in advising on green choices. But the best way to reduce waste is prevention: consume and throw away less - whether or not the material is biodegradable, Wong says. That's why the farm charges customers HK$1 for the biodegradable bags stocked at its souvenir shop and organic vegetable store. 'Our goal is to encourage consumers to bring their own.'

Housewife Erny Cheung Po-lin sets a good example of what can be achieved with a little perseverance. Whenever she shops at her neighbourhood wet market in Tuen Mun, the former merchandiser brings her own plastic bags for vegetables and a container for meat.

An eco and health-conscious consumer, Cheung also keeps informed on news about potential risks from pollutants and depleting natural resources. 'Everything is so readily available, we have forgotten how to cherish our resources,' she says.