When you go out to eat, you often have leftovers, right? And those leftovers usually go home with you in a container, either plastic or Styrofoam, which you then have to recycle or throw away. What I do is carry a bag containing a few empty containers of different sizes in the trunk of my car. Then if we eat somewhere, I bring the bag in with me. At the end of the meal, out come the containers, and leftovers get packed up without using new to-go containers.
Likewise you can bring your own mug when getting coffee, even your own plate, bowl or utensils if you're not eating at a sit-down place. Here's a list and video by Sustainable Dave Chameides, who's got an awesome blog, 365daysoftrash.