I generally try to pack out what I can, within reason, with an emphasis on what I can recycle. On beaches I always make a special effort, because I imagine it otherwise joining the Pacific Ocean Garbage-patch and choking sealife.
My most dogged effort, though, was packing out a used pampers diaper (double wrapped in my spare ziplocks!) that I found in Center Basin on the JMT, carrying it over 13,000' Forester Pass, and then over Mt Whitney, about 32 miles. I tried to pass it off on a ranger along the way, but she was having none of it.