a) One who eats bread at a meal should not leave the place where he ate and go to another place so that he will not forget to say Birkat Hamazon (Grace After Meals). Only after he has recited Birkat Hamazon, he may leave.
b) One who forgot and left for another place before he recited Birkat Hamazon: If it was unintentional – he may recite Birkat Hamazon in the place where he is, and if he left intentionally – he should go back to the first place and recite it there.
c) One who has to leave the place where he is eating for urgent reasons and wants to come back and continue his meal: If he is going to perform a Mitzvah, he may go and then return to his place and continue eating, but if he is going for a voluntary reason, he should recite Birkat Hamazon before he leaves. If he does not intend to return to his place, even if he is going to perform a Mitzvah he should recite Birkat Hamazon before he leaves.
d) The Sages say: “One who does not leave bread on his table will never see any indication of blessing.” This means that the bread left from the meal should not be removed from the table until Birkat Hamazon has been recited. Similarly one should not remove the salt from the table. Even if the bread was finished one should leave the crumbs which fell during the meal and not clean them until after Birkat HaMazon.
e) Shlomo Hamelech wrote regarding the woman of valor: “Her husband trusts her in his heart and does not lack for goods”. The Ben Ish Chai explains: This means that a husband trusts his wife to sweep the floor after meals and to remove all the crumbs which have fallen there so that people won't step on them, as one who steps on crumbs causes poverty both for himself and for the members of his household, G-d forbid.
f)There are people who place the leftover bread in a bag and hang it on the garbage can but there are two problems with this: 1) It is forbidden to hang bread as this can cause danger to a person. 2) Many times the bag falls and splits and the bread will scatter and will be degraded. It is better to place the bread in a bag and close it and leave it in the garbage can.