How do you keep a bin bag open

[Beabea]

I have a dust bin outside the back door. I want to be able to keep the bin liner open when you throw rubbish/nappies in it. As soon as you put one item in it collapses in the bottom of the bin. How do you keep it open? Can you get large elastic bands? If I have the rubbish in one hand then lift the lid I haven't got a spare to open the bag. Petty I know but irriates me no end!

Thanks

I keep meaning to tie a length of elastic into improvised elstic band for just this purpose!

Thanks I will have a look in the sewing box. I don't sew, DH does!!