The green movement encourages us to reuse shopping bags - to not keep consuming more and more and more plastic bags.
Back home, I was working on this. We certainly reused or recycled all our Giant, Safeway and Washington Post bags. I bought a couple re-usable Giant bags and more than half the time remembered to take them into the store with me.
In Belgium, I always remember. If I don't I have to figure out how to juggle all my items in my hands and arms until I can get to the car. This applies to any store in which one purchases anything - grocery, hardware, clothing, office supply, etc. (Souvenir shops will usually provide bags, they are used to Americans.)
At the grocery store one can buy a re-useable bag, but they aren't that great and if you buy new ones every time, the cost adds up quickly.
I own five Giant bags, one is a cooler bag. I use them constantly. I even bring them to the US Commissary (the one store that does give away bags).
I'm in the habit of remembering my bags and using them. Maybe I'll even keep the habit when I return to the US....