Last year I went to a Christmas Eve service with my wife (a member along with me) and my family (not members) at their local Presbyterian church. I wasn’t sure whether it would be appropriate or not to take their communion (grape juice, not wine) when it was offered, but I did participate. My wife didn’t. I felt very out of place and uneasy about the whole thing and wasn’t sure how to respond. I used to be a mainstream Christian and took the communion often and thought that it was acceptable in that case. My wife disagreed, saying she didn’t share their faith and that we shouldn’t participate. What should I do in this situation if it arises again in the future?
Partaking of the Sacrament is an ordinance in the Lord’s Church where we renew the covenants we made with Him at baptism. Priesthood authority is required to make the ordinance binding. If you attend another Church, where the Priesthood does not officiate in the Sacrament or communion, then the ordinance is not binding. So, from this perspective there would be no need to partake of the Sacrament.
Beyond this explanation it is a personal choice. For instance, we allow all who attend an LDS Sacrament Meeting to partake of the Sacrament if they choose to do so, even if they have not been baptized into the Church. It is for you to determine whether or not you should eat the bread and drink the water (or juice) at a different church’s service. My only suggestion is that you make it a matter of prayer.