TOWEL RACKS and TP ROLL inside recessed cabinets between the studs. Also, why not store plunger + toilet bowl cleaning brush etc in there too, behind a cabinet door? DIY: How to Build a Cabinet Inside the Wall -
Guest bathroom storage idea (above toilet). Wall cabinets are highly recommended for small bathrooms. Unlike floor storage units that occupy a lot of space, these wall cabinets won’t make the space any smaller than it already is.