Grocery bags for sure. For garbage, for kitty litter, for assorted uses, including I keep a bag of the sizes and shapes that I don't use and take them to my mother-in-law whenever we go visit -- she walks her dog with a bunch of other people in a field near her place, and there's usually a bag or two of "doggy poo bags" hanging on the fence for people to use for scooping.
Twist ties -- yup. As long as they still twist, they still tie!
Plastic produce bags for assorted uses, including bread products that arrive in paper.
I'd love to save the liners of cereal boxes, too, but don't have enough uses to spare them the space.
What doesn't get reused, mostly can be recycled.