I work in a supermarket and I have seen the effect the bag charge has had on habits. You'd be amazed at how many people used to want bags for everything - thin plastic bags to put birthday cards in, thin bags for clothes, separate bags for each individual fruit/vegetable, bags for a pack of gum or pack of batteries ... now people would rather juggle their items or stuff their handbag before paying for a bag.
I have had people come to the kiosk with a bottle of water, sandwich, bar of chocolate and ask me for "a small bag". As soon as I say "Sorry, we only have 15p bags for life" they can suddenly carry their lunch rather than pay the extra 15p, whereas in the past they would have taken one for the sake of it.
Same on the checkouts, we can provide the really thin plastic bags for raw meat but we found that if cashiers asked if a customer wanted the raw meat in a separate bag then they would usually say yes, but if we dont actively ask (but still have the bags clearly available) then customers rarely ask for their raw meat to be bagged separately because most people arent bothered unless and until you ask them.
I use a wheeled shopping trolley as it's easier for heavier items as I dont drive (and no way I'm weighing down my shoulders with bags full of bottles and cans for the walk/bus ride home) so I keep a couple of extra reusable cotton tote bags in the trolley to be used for food items and a couple of mesh bags (I use the drawstring bags used for washing delicate items) for fruit and veg when I specifically do a food shop. I just weigh the fruit/veg individually in the department and put them all in the same bag with all the stickers for the cashier to scan.
I also keep at least one canvas tote (folded into a pouch smaller than my purse) in my handbag and another in my work locker. That way if I need to pick up bread/milk after work then I have a bag handy or if I pop into town to buy a few small items and they wont fit in my handbag then I have a bag to put them all into. In the last year I'd say I've had to purchase maybe 10 plastic bags at most, and that's usually only when I've been picking up stuff for someone else with my own shopping and wanted to keep it separate or when I've run out of bags. These bags have all been reused - eg DD keeps one in her school bag for wet stuff (it rains a lot where we live) or if she has to bring stuff home that doesnt fit in her bag - before eventually being used instead of bin bags when they have worn out too much to be useful in any other way.