What it means
Fast little call to get out of a chore or any grim job, basically the Aussie and Kiwi version of not it. Someone mentions taking out the bins and suddenly everyone’s yelling it like they’re back on the school oval. First to say it is safe, last one standing gets stitched up with the task. Childish, yes, but weirdly effective.
Usage examples
"Who’s washing up after the barbie? Bags not. Too slow, bro, you said it last, so you’re on plates while we sink a stubby."
"Bags not doing the washing-up tonight."
"Someone has to tell the boss. Bags not!"
"Right, who's cleaning the ute after footy? Bags not. I said it first, so pick another mug."
"Mum said someone has to walk to the dairy for milk and all three kids went bags not at the exact same second."
Where it comes from
It grows out of bags, a schoolyard call in Australia and New Zealand for claiming something first, the same family as bagsy. Bags not is the dodge version of that move. You call dibs on not doing the grim task, and whoever's too slow gets stuck with it.