The Rama (178:2) writes that when it comes to bread meals, the rules of Shinu Makom (changing locations) are more lenient. Generally, if one eats a snack (e.g. a bag of potato chips) and then leaves his house before he has finished eating, he must make a new bracha on the same bag of chips when he returns to his house, even if it is only a few minutes later. If however, he is in middle of a meal in which he washed and ate bread, he is not required to make a new bracha when he returns to his original place.
The Mishna Berurah brings down a Magen Avraham that says that this halacha only applies in instances in which the person already ate a k’zayis of bread (178:28). If however the person has not yet eaten a k’zayis of bread, he must make a new bracha on the bread if he wants to resume his meal at the original location.This is an important halacha to keep in mind on Shabbos, at weddings, or other simchos during which people tend to eat a piece of bread smaller than a k’zayis at the time of making the hamotzei and often change locations before eating a full k’zayis of bread.
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