While on the Camino I have met a number of people for whom this is such a deeply important, meaningful and, therefore, potentially controversial topic. In fact, there are a few folks I have met for whom the relationship with the church , and how and to whom the church extends it's welcome, is a source of significant pain and confusion.
There is, of course, a fairly straight up, doctrinal answer about communion: if one is Roman Catholic, or part of a tradition in full communion (you likely know who you are) with the Roman Catholic Church then it's pretty clear. There are circumstances in which Roman Catholics who are otherwise in good standing may not receive the sacrament of holy communion (you also likely know who you are).
So many of us who are Catholics or non-Catholics, Christians or non-Christians experience the Camino as intensely communal, those for whom sacrament becomes part of our daily walk; the Camino explodes with meaning (and, therefore, I will go out on a limb here and call this the presence of the holy, even the Holy One). Some of those outside the Catholic communion feel drawn into the mass, to come forward with other pilgrims.
A cold beer shared with a fellow pilgrim, an attentive ear, an act of kindness received or given, a long stretch of road when one is confronted with oneself and ones own thoughts (and history), a lively, honest conversation, might end up being an experience of the transcendent, dare I say, a sacrament. Going to mass is one more way some of us Pilgrims of all religious (and non-religious) stripes try to stay open, to be mindful. And mindfulness is key, in my estimation.
A very elderly priest who seemed to be shrinking before our eyes spoke softly, barely audibly, into the microphone in front of a standing-room-only crowd at the pilgrim's mass in Roncevalles last April. The old priest said, "If you desire to be at peace with God, at peace with your neighbor and at peace with yourself, you are welcome at the table." It was an offer few, if any, refused.