I hike to my local market for goodies on occasion and instead of carrying 8 plastic bags full of food back over the 2.5 kilometer trek, I carry a pack (a Karrimor Sabre35 to be exact because of the amount of food I can stuff in it) with me into the store.
This use to upset the store staff, and even caused some confusion at the register because I would have to pull everything out of my bag that I had put in while shopping (this place only has hand baskets -no trolleys) and a few times I had pieces of personal kit I had forgot to remove beforehand.
Now the staff know me and I only get looks /hassles from other customers who think they have just caught me trying to nick a tin of beans. Probably the most excitement for them in a long time...