Graphing calculator of Rlyeh - A graphing calculator that graphs Alien Geometries. We don't have anything that's calculator-like, do we?
Sponge of holding - Appears to be an ordinary, dried out sea sponge but teleports the liquid it's soaked in into Another Dimension, and disgorges random types/amounts of said liquid when it's wrung out.
Guy Made of Sound - A guy made of sound. So yeah.
Vorpal pencil - Appears to be an ordinary wood-and-graphite pencil that, when sharpened, gains a point sharp and fine enough to pierce 6cm thick steel. It's not indestructible; it can be broken and resharpened.