I never fill them, I use them as rubbish bags. Unlike a lot of charities, BHF doesn't deliver bags, people ask for them in the shops if they want them. If people can't bring their donations, BHF are happy to collect.
It might surprise people what does get donated! At least if clothes are unsaleable individually, textiles can be sold by weight. Broken ornaments, cracked and chipped ceramics or glass can't be sold, similarly opened bath and cosmetic products, broken toys etc. On the other hand, some donations are surprisingly valuable. We get designer shoes and clothes, silver and gold jewellery, expensive household items, lovely toys. Some of the better items go to Ebay, If anyone has time on their hands, volunteering is a great way to fill it.