Mission Australia Illawarra retail service manager Justine Fitzgibbon has encouraged residents to dig deep, with op shops across the nation struggling with dwindling donations.

Of course, she said, it's always a good idea to check your pockets, purses and pants before giving them away to charity.

"Our volunteers have found all sorts of things in pockets and purses - from loose change to used hankies and even an iPhone," she said.

"Once we found some war medals in an old suit and couldn't track down the owner so we ended up donating them to a local RSL club.

"We get about 700,000 kilos of clothing donated each year to around 50 clothing bins and seven retail outlets across the Illawarra and our main Bellambi warehouse, so it is hard for us to find the owners if something valuable gets left behind."

National Op Shop Week, an initiative of the Do Something! charity, grew from research showing that more Australians were buying clothes from op shops, but fewer were donating.

National Association of Charitable Recycling Organisations CEO Kerryn Caulfield said charity op shops were experiencing their lowest stocks on record.

Mrs Fitzgibbon said that was reflected in the region, with a 30 per cent drop in donations in the Illawarra over the past year.

"We are really struggling at the moment," she said. "The main factors are that the quality of the stock is not as good as it used to be and that people are holding on to clothing for longer as finances are tighter.

"The other problem is that people are dumping rubbish at our bin sites which obviously upsets local residents and we are being asked to remove our bins. Ten years ago we had about 80 clothing bins throughout the region, now that's down to 50."

The Illawarra's Big Heart op shops are among 2000 Australian charitable stores listed on the OpShopWeek.com.au website.

To donate unwanted clothing, soft toys, bed linen, blankets and other items, type in your postcode for the closest drop-off points.