As all the above, most of us have purpose because of little things that makes us important/significant to others: family, friends, lovers, pets, children, people who likes or respect us. Even having enemies(they may vary from people or life situations to states of mind, addictions or health issues) gives us reason to exist. Share, man, share. We rarely live for ourselves, a person who lives that way is just self-destructive.
Last time I gave a surprise birthday to my little 6 year old niece. That time she went back from school crying because her teacher had scolded her by mistake. She knew she wasn't at fault, but the feeling of being scolded before her two best friends and entire class was unbearable. When she entered sobbing in her room, that was filled with so many colorful balloons they started to get out from the door nonstop. She was ecstatic, jumping with her two friends she was with, completely forgotten the earlier pain. Her friends yelled "Your uncle is sooo awesome". Then she hugged me with all her might while giving me thanks for being her best birthday of her life. I felt like i was given superpowers, so good it was.
Do you guys remember what did you want to be when you grow up? I wanted to be like Gramps and my Granduncle, two guys who raised me as a son. I wanted to be a Mentor. I wanted to be a friend. I wanted to be a Father. And sometimes I am, maybe without knowing it.
I was born sterile, maybe not to be father of one, but to be father of everyone.
So my advice for a purposeful life is:
-Have a role model
-WHY do you want to be like that role model
- What do you need to know/be/have/do right now to begin to be like that
-How are you gonna do it
You don't have to take my words too seriously, I'm not sure if I'm right or wrong, so ask other people what they do to have a purpose in life. Ask your friends, people you come across, your chat buddies, anyone who can give you a better response.