When I shop by bike, I bring two kittiers, as well as a bungee net if I need to secure stuff on top.

(like tsl) I have never had a problem going through the store with my kittiers in a cart, filling them as I go through the aisles, emptying them at checkout, and filling them again as the groceries are scanned by the checker. Usually have a nice conversation with the checker about how cool they are.

Also one of mine is never completely empty, there will always be a few small tools, sunglasses, gloves, assorted old receipts and other garbage, hanging out on the bottom. I have never had anybody challenge me or check that I didn't pull everything out, but since I am not stealing anything, I would be happy to submit to a check, and embarrassed and apologetic if they found some small thing I forgot (baggie with 1 tsp of some spice from the bulk jars?)

Also, I sometimes hit multiple stores, which means I carefully secure items with their receipts in their shopping bags, so in case of products that are available at multiple stores, I could show on the receipt, "I bought this there, just half an hour ago".

PS here in San Diego, we still have plastic & paper available everywhere. I think the ban doesn't take effect until July. But I did read once that in Ireland, they had a problem with littered plastic shopping bags all over, a small surcharge per bag solved that problem very well.

Meanwhile, some hippie/healthy/green kinds of places (i.e. Henry's aka Sprouts) will take like a nickel off your bill for each of your own bags you bring in and reuse. So that's kind of like a 5 cent cost per bag already.