Us humans, are the only species on Earth that seems to keep and accumulate a greater variety of objects than all other species combined. 

For instance, we never recall seeing any photos of puffins carrying anything in their beaks except patches of grass or small fish. They seem to only carry and collect what they truly need. 

Humans are more intelligent, which is probably a very good explanation. Our highly wired brains seem to need more or, sometimes, just want more.

Although it must be said—hopefully in an amusing way—that sometimes we seem to unable to distinguish between what we truly need and what  we can reasonably consider just "stuff".  Whimsically enough, one of the synonyms for "stuff" in the dictionary is "junk".

It’s important to remember, now not in humorous ways, that "junk" can sometimes interfere with our "freedom", which is definitely more important than "stuff" :) 

Photo by Steve of Atlantic Puffin in Iceland