I've found that the easiest switches to make were straws (the small collapsible one, $10) and the bar ($11) and refillable shampoos that work surprisingly well.
When we get our groceries delivered (still avoiding indoor outings due to COVID), there are plastic bags involved. Since going to the Saturday Morning farmer's market though, we've stopped buying as much that way so I think transitioning to mainly whole foods will solve that problem by itself.