The Kitchen Knife is a reasonable secondary backup weapon (or even primary if you prefer knives). It is light and has the 'Jaw Stab' attack which can kill a zombie instantly if close enough and timed correctly. However it is not very durable and with deteriorate on average every two zombie attacks, giving a full condition knife an average of 20 zombie attacks/kills and considering its weight, is probably better suited as a backup.
The Kitchen Knife can be found in kitchen cupboards in many houses and in a few other places ingame. It is a one handed weapon which means you can carry a second bag in the secondary slot (assuming the first bag is on a characters back).
The kitchen knife is a single attack weapon, so it is best if used in single combat or if zombies are relatively spread out when attacking.
The kitchen knife is also used in the preparation of some foods such as cutting watermelon slices.
Its tree/door damage is negligible. (1 tree, 1 door per attack).