Pack it in, Pack it out
And on the way out, when the panniers are light, try to pick up litter left by others.
Reduce litter at the source
When preparing for your trip, repackage food into reusable containers or remove excess unnecessary packaging. This makes less to pack in and less to haul out.
Trash is the non-food waste brought into the backcountry, usually from packaged products. The best bet is to carry out all trash. Some paper items can be burned in a campfire, but much of the pager packaging used today is lined with non-burnable foil or plastic. These paper products should be packed out with the cans, plastic, foil and glass.
Garbage is the food waste left over from cooking. Careful meal planning can easily reduce this waste and minimize the amount of leftovers. In the event you do have leftovers, they should be eaten later or put into a plastic bag or other container and packed out. Burning food waste requires a very hot fire and burying this type of waste is inappropriate because animals will dig it up if it is buried (see special considerations for bear country). Animals, from squirrels to bear, habituated to humans as a source of food can become a nuisance or even a threat to humans. Always pack out everything you brought into the backcountry when you leave.