To avoid forgetting, I now keep a shopping bag in my handbag. It is very small when folded and doesn't take up much space in my handbag. I bought it at Guardian, about RM6 (I think). But you could sew one...
When open up, quite big.. carry quite a lot of things.
Repurpose pillow case as shopping bag:
I have this unused pillow case and turned it into a shopping bag... Quite happy with the result.
Another shopping bag added to my handbag. :)
Useful way of organising plastic bags:
If you have lots of plastic bags at home, fold them neatly and keep a few in your bags and many in your car. :). There are many ways of folding them.
1) Triangle (my favourite) :
How to do:
2) Square : http://www.doflick.com/ViewVideo.aspx?vId=260