I am a big fan of reusable grocery bags these days, and am forever on the hunt of the most convenient varieties...Canvas grocery bag/tote from happyfamily.
Riptsop nylon bags in brilliant colors from kootsac. I must say, ripstop nylon is my favorite at the moment - strong enough to hold a sac-full of heavy groceries without a care, and crushable enough to fit in bulk in the inside pockets of my diaper bag without taking up precious space.
Gorgeous reusable gift bags made from Indian sari silk, from tweedylane.
Light-as-air produce sacks from LoveforEarth. And don't they look fabulous?
Graphic veggie bags from wonderthunder.