I always used a backpack when living in NYC because I could ride my bike instead of lugging all of that heavy stuff on foot for 6 blocks. These days I have a really big sturdy bag from some French store called "ED" (a hand-me-down) and a normal paper-bag-sized Trader Joe's bag that I bought for a dollar. I fold them up neatly and they live where the excess of plastic used to come spilling out from. Then when I get a lot of groceries (maybe once a month or so) they put the overflow in some new bags for me to take home to use for recycling and lining the bathroom trashcan. That is usually plenty for one person to get by on. Plus, I've discovered that most stores give you some kind of little reward for bringing your own bags - a lot of them give a 5 cent discount or something on that order and TJ's gives you an entry into their weekly raffle for free groceries. Nobody ever cares or notices that the bags don't match the store I'm in.
As I'm finding with a lot of other things in life, the less I worry about what people might think or how I'll work out what I'm supposed to do when I change how I do things, the more things seem to work out on their own and the more desire I feel to go out and try new things. The self-confidence also builds up from the most unexpected things, like being able to go to a store with my own bag and helping the cashier bag the groceries. Somehow, that makes me feel really able and strips me of shyness and awkwardness I might otherwise feel standing there getting waited on the usual way, complete with disposable bags full of my food being piled into the cart.
As a person who's never found environmentalism to be doing any favors for the earth and the creatures that live on it, I have to say that this practice just makes sense. Actually, a lot of the things environmentalists say make sense, only it's hard to see it through all of that loud, obnoxious activist-speak. Why not do things like this because they are smart, efficient ways of doing things?
Something new I've adopted is reusing my ziplocks and other plastic bags that come as packaging. Other than the stuff that gets really messy or unsanitary (like for meat or sticky things), one little ziplock can go a long way - especially if you're the type to pack the same kind of lunch every day. I use the same two bags for the chips and berries I bring to work with me and usually they last 2-3 weeks before I get something messy on them or they tear. Sometimes they just fill with two many crumbs of different things and I toss them. Still, for one bag? That's pretty good. There are also all of those resealable or tie-able plastic bags you get for schredded cheese, loaves of bread, tortillas, etc. I hang onto those and use them as lunch bags instead of the grocery bags because they're more appropriately sized and I'm keeping them out of the landfill for another day. I imagine they'd be good for kitty litter and stuff like that, too. Lining the trash, though, I think is still a job for the plastic grocery bags. They're good at it. Plus, you don't have to feel so bad about that anymore anyway:
some clever kid in Canada figured out how to make them degrade faster!
In any case, I like this reusable bag idea more for the effects of reducing demand for production. People make and keep too much stuff and it crowds out our lives.