I’ll begin by saying that people with a preference for bladed weapons are entitled to their opinions. They can be completely appropriate depending on their use, and I think space for at least two small, folding ones should be included in a B.O.B.
However, I still have serious reservations about the use of bladed weapons in the event of a zombocalypse. If you’re looking at going at human targets then knives are fine, but we would not expect those weapons to be more lethal to zombies than blunt weapons, especially when they are not in the hands of someone skilled in their use. Still, something like a high-quality aluminum bat might work best when considering potential knockdown or incapacitation, durability, length, and reliability. All of these factors would be essential in choosing a backup melee weapon. Space might be an issue, but they are typically lighter than shovels or sledgehammers and have better range and lower penetration potential than picks, axes, or hammers.
Along with Nightside, I would use the butt of a gun before using a knife. First, I would not want to be near these things. If you’re that close to one, you’re likely to be that close to more. Also, I would not want to get their blood anywhere near my person, and a cutting weapon might get some on me, particularly if I were looking to make head wounds. The weapon has a danger of sticking or breaking off in the bone, and that’s too risky. I would never use the spiked knuckle feature on trench knives, because I would never want to get a part of my body that close to a zombie. The only purpose I would keep a knife for is utility.
Of course, if you’d plan on going for short-range combat with either a bladed or blunt weapon (e.g. hammers are great if you need the space, but they’re too short), I would suggest using something in your off hand to block bites. Since most people don’t own shields and shields can be weighty and take up a lot of space, I would suggest something you have in your homes. This may sound really funny, but a plunger could fulfill that use admirably. If you can use a short-range melee weapon with confidence, then you can probably use the plunger to cover up their mouth and jaws for as long as it takes to get in for the close kill. Also, if they try to bat away your weapon, they’ll be more likely to bat away the plunger as it will make contact first. Chances are that this will leave them open for an attack from your primary melee weapon of choice.
If the zombies are such that melee combat isn’t as risky (movement speed is a big factor), a plunger could be a great choice. They are relatively durable, easy to find, light, and you suffer almost nothing from ditching them.
Plus, the comedic value of the weapon is sky-high.