It’s hard to answer your question without more information about the situation, but here are the basic principles involved: One is supposed to genuflect whenever one passes before the Blessed Sacrament reposed within a tabernacle (General Instruction of the Roman Missal 274). One is also supposed to give a bow of the body whenever one passes in front of the altar (Ceremonial of Bishops 72).
The former discipline takes precedence over the latter. Thus, if the Blessed Sacrament is in a Tabernacle on or near the altar, one genuflects and does not bow. If there is no tabernacle on or near the altar, or if the tabernacle is empty, one bows to reverence the altar and does not genuflect.
The Church’s laws state that one is supposed to make the appropriate sign of reverence whenever one passes in front of the altar or tabernacle. The exception it makes is for people who are carrying articles in procession (e.g., a cross, a candle, book of the Gospels). These people are not supposed to genuflect or make a bow of the body (Ceremonial of Bishops 70). A bow of the head, on the other hand, would be all right, though the law does not seem to mandate it specifically in this circumstance.
I would assume that the same would apply when carrying something in front of the altar (e.g., cruets, a ciborium, etc.) to avoid the danger of dropping the article or spilling its contents. So if you are carrying something in front of the altar, I would advise you to neither genuflect nor make a bow of the body, but merely a bow of the head. This is especially the case if you are carrying the Lord’s body or blood.
In former years, when Communion rails were common, during distribution of Communion the priest would pass in front of the altar and tabernacle without making a sign of reverence. His back would be turned to them, the tabernacle often would be empty and left open to signify this, and he had Jesus in his hands at the moment, which required his utmost attention and care.