Old shopping bags become bin liners. We do not ever buy bin liners.
Smaller plastic bags from the supermarket or greengrocer wrap vegetables in the refrigerator, but also serve in place of gladwrap to cover food before serving.
More sturdy bags are used to gather the recycling. They are also handy for packing clothes on a car trip. Suitcases are hard to stuff in the boot, while plastic bags squish happily. Small carry bags make ideal rubbish receptacles, and I try to have a few small plastic bags in the car for emergency use.
On longer trips with a suitcase, plastic bags segregate dirty clothes from clean.
Ziplock bags from the bulk food section of the supermarket are washed. Then we reuse them in lunchboxes, to seal small opened packets, or (my newest discovery) to marinade or brine meat in (you use a lot less marinade that way).
Of course where we can we use a tough bag of our own, eg at the market, or at Pak’N’Save. So we don’t get as many plastic grocery bags as we might, but enough pile up through incidental purchase that we still have quite a collection (stored in another plastic bag, naturally).
I cannot recall paying actual money for a bag for quite some time.
How do you reuse plastic bags?