any box of tampons
A cuboid.
A tent
The diagonal of a unit square, for example, is radical(2).
A foreign brick.
A gaming die.
roof
A building would be a perfect example. If you simplify the details of a building, it becomes a rectangular prism. If you specifically mean a "square" prism, that would be a cube, an example of which would be a Rubik's Cube or a few dice.
A real life example is a Toblerone chocolate bar which is in the shape of a triangular prism.
Roof of a house
tent
any box of tampons
a cabinet
A cereal box or a t.v. [not flat screen] or a book.
A solid brick is a rectangular prism. (this one example of many)
A basic camping tent, a house roof, and the iconic Toblerone box.
A cuboid.