I've found a couple of mods that do this in theory, such as Auto Pickup and Instant Barrel Loot.
Although these mods work okay, I dont like how all barrels and road signs become 1 Melee hit from destroying the entity.
I would like to keep the vanilla feel of hitting the barrel a few times to destroy it but still receiving the loot in your inventory without picking it up.
I have seen this live on some servers but cannot find the mod they are running. Does anyone know of a mod that does this?