The 2x4 is a plank of lumber you pick up off the ground and swing until it breaks. It is weak on its own, but crafting recipes turn it into the Spiked 2x4 and the 2x4 Axe. Treat it as raw material for something better.
Use a plain 2x4 only to finish off a stray Swarmer or a downed human. It breaks quickly, so craft it up as soon as you carry nails or a saw blade.
The 2x4 Axe has the same damage and durability as the Bat Axe, Fence Post Axe and Stool Leg Axe. Pick whichever wooden base you find first. The Ripper Axe uses a 2x4 plus nails and 5 scrap.
Field Repairs lets you fix melee weapons with scrap, which keeps a crafted 2x4 alive longer. Hard Hitter and Home Run both raise damage for crafted and found melee weapons.
Baseball Bat
The Baseball Bat is a common wooden melee weapon you find lying around. On its own it breaks fast, but it is the base for the Spiked Bat, Bat Axe and Superior Club. Keep one handy for crafting.
Baseball Bat Axe
The Baseball Bat Axe is a crafted melee weapon: a wooden bat with a saw blade bolted on. The recipe sits in the bunker of the fourth Ambush Camp you clear. It hits much harder than a spiked bat for almost the same parts.
Boot Knife
The Boot Knife is Deacon's always-equipped blade, and it never breaks. It handles stealth kills and finishes grapples when your melee weapon is gone. Skills make its combos hit hard enough to rely on.
Fence Post
The Fence Post is a common wooden melee weapon you pull from the world. It is weak alone, but it can become the Spiked Fence Post or the Fence Post Axe. Use it as a crafting base when you have nails or a saw blade.