Yesterday, my mantra was "It is good having shit to do." I think it's true. I was fully-engaged with the day from start to finish. And it was good. Not a lot of time to reflect, lots of time getting from one place to another. The "doing" becomes the "meaning," and the "purpose."
I remember reading something like "being an alcoholic gives one something to do." You are always swimming towards the next drink. I think it's the same with being a junkie, you are always searching for the next fix. Your addictions becomes the doing, the doing becomes the meaning.
Best to pick your addictions & poisons wisely. I am hung up on coffee. Massive quantities of coffee in the a.m. Also music, totally addicted to listening, playing, thinking & reading about music. I can fill my days with coffee and music and I am full.
I force myself to be engaged with the world too. That engagement is the meaning and purpose. Right there.