If it's going in the wall or on the wall (or the ceiling come to that), you will find a box to suit in this category, including dual boxes that let you fit two single accessories side by side and a 2+1 box that lets you put a double accessory like a double socket neatly alongside a single accessory like a spur, timer or switch. 

Make sure you order a box deep enough for your accessories. USB sockets for example often require at least a 35mm deep box.