Jug bands definitely include someone playing a jug, but it also means a group of people playing nontraditional or makeshift instruments, with or without a jug. Sometimes traditional instruments are mixed with unconventional instruments, and these bands are also called skiffle bands - especially when there is no jug.
An empty whisky jug is the instrument of choice - often emptied during or just before the performance. By blowing across the top of the jug, the air inside vibrates producing a deep and funky sound in the tuba range. The instrument is often called "the poor man's tuba." A beginner can usually produce only one note - if that. A little practice enables you to play the tonics and fifths (C's and G's) of roughly two octaves. Skilled players can get more notes in the two octaves. Pitch is controlled by the angle of attack and the embouchure, which is the position of the lips and mouth.
The washtub bass is rarely seen outside of jug bands. The instrument consists of a washtub, a broomstick and a wire. The wire is attached to one end of the broomstick and to the center of the washtub's bottom. The washtub is turned upside down and usually held in place by the player's foot. The other end of the stick is held against the rim on the bottom of the washtub. The played holds the broomstick in place and varies the tension to make different sounds. A good player can get a respectable bass line out of the instrument.
The washboard is one of the few traditional jug band instruments that has been taken up by other types of musical groups, including zydeco bands. A rhythmic rasping sound is produced by running something up and down the washboard. The sound is determined by the instrument that is used. Wood, metal, plastic and bone are all used to produce different sounds. Sometimes the sounds are reminiscent of similar instruments used in Latin American music.
Kitchen utensils are often seen in jug bands. Musical spoons are a typical example. An experienced jazz or rock drummer can produce interesting rhythms from several inverted pots and a couple of wooden spoons. Kitchen instruments are most often seen when jug bands are formed at home and performing there instead of in public.
Traditional instruments are often combined with "found" instruments in junk bands. The guitar is the most common instrument, because it goes well with other instruments and is easier to find. Kazoos also go well with jug bands because they're easy to play and comical sound fits in well with the whimsical nature of jug bands.