Bread is often synonymous in Scripture with food in general, as it has historically been the principal sustenance and a common feature at meals. And with bread in particular the custom until more recent times was to tear a loaf into smaller portions for all to eat. This is seen in scriptures such as Luke 9:16-17, where Jesus broke the bread into pieces before feeding the five thousand. Note that "broken pieces" were left over.
Furthermore, Jewish meals of Christ's day customarily began with a blessing over bread and then a breaking apart of that bread for distribution. As Barnes' Notes on the New Testament states of the breaking of bread in Acts 2:42 and 2:46, "It would rather seem to be implied that this referred to the participation of their ordinary meals. The action of breaking bread was commonly performed by the master or head of a family immediately after asking a blessing" (note on Acts 2:42).
You should also read carefully Acts 27:33-38, where bread was broken after giving thanks in the process of having a meal for nourishment, with those partaking receiving enough to eat.
It is this same meaning intended in Acts 2:46, where if the rest of the verse is understood in context it is clearly referring to a meal. This verse states that they attended the temple daily and then returned to their private homes to share a meal. The New Century Version renders this, "They ate together in their homes, happy to share their food with joyful hearts." The Good News Translation states, "They had their meals together in their homes, eating with glad and humble hearts."
As with all Jewish meals, the Passover meal likewise included the blessing and breaking of bread—in this case, unleavened bread as a required part of the ceremony. During the Passover meal before His death, Jesus incorporated the blessing and breaking of bread into a new Christian observance of Passover. On this occasion, observed once each year on the same night, the breaking of unleavened bread symbolizes Christ's sinless body being broken as an important aspect of His sacrifice for our sins.
Yet the common phrase "breaking bread" still referred to eating meals generally, as it did in Acts 2:46. Interestingly, this custom is preserved for us today in the commonly used English words "company" and "companion." These are derived from the Middle English compainoun, which came from the Old French cumpaignon, literally "one who breaks bread with another," from the Latin companis, meaning "together with" (com) + "bread" (panis), or someone with whom you were sharing bread or meals.