The table should be cleared before bentching of all dirty dishes, used cutlery, and empty bottles in order to show proper respect for bentching. However, the tablecloth should remain, as well as some remaining bread. The remaining bread on the table allows for the brachah of Hashem to rest on the individual. Another reason for leaving the tablecloth and some bread on the table is to indicate that we are thanking Hashem during benching for the food that we just ate. If there is no left over bread, sizeable crumbs are sufficient. If there was a complete loaf on the table, it is best not to remove it until after benching, but bringing a full loaf of bread to the table specifically for bentching is actually asur, forbidden, according to the Shulchan Aruch. There is a custom to remove or cover all knives on the table before bentching on weekdays. (Some poskim hold that this does not apply to plastic knives.) However, on Shabbos and Yom Tov we do not have to remove or cover the knives, nor should we do so.