Everything you eat is the body of Christ and everything you drink is the blood of Christ, therefor and according to the apostles eating and drinking without examining/judging yourself first is eating and drinking damnation and guilt in the body and blood of Christ unto yourself.

1 Corinthians chapter 11 verses 25-30 speaks about that.

So basically it's not eating a spacial cracker nor drinking special wine who must be prepared and administered by a priest but rather every meal we have and every thing we drink.