As I understand it, both of those are US variants. I myself say "rubbish bag", but unless we want to wade into types of waste bags, they all still mean the same thing, so +1 to:
Aliasing trash_bag -> waste_bag
Aliasing trash_bags -> waste_bag
Aliasing rubbish_bag -> waste_bag
Aliasing rubbish_bags -> waste_bag
Aliasing garbage_bag -> waste_bag
Aliasing garbage_bags -> waste_bag
Aliasing waste_bags -> waste_bag
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