Drums are the backbone of any live music act. They provide the rhythm along with the bass guitar for any style of music including rock, funk, and R&B. Only electronic styles of music forgo drums in favor of prerecorded drum loops and samples. A five-piece kit is usually the minimum, with a snare drum, kick drum, a few rack toms and any cymbals necessary. A high-hat, a ride cymbal and crash cymbals are usually needed as well.
Guitars and amp are almost always seen in a live setting whether the music is calypso or heavy metal. One guitar rig will usually suffice for more mainstream styles of music such as pop or light rock, but heavy metal bands usually incorporate two guitars for lead and harmony guitar lines. A combo amp or a nice half-stack, which includes an amp and cabinet, will suffice for most live shows with proper PA support. Effects units and the actual guitar used are provided by the individual guitarists and vary greatly among these types of players.
Bass plays a major role in the rhythm section. It is considered the bridge between the melodic side of guitar and the percussive drum line. Bass plays an important role in reggae and rock music and is almost always seen in a live setting. Hip-hop also uses live bass in some settings, but it can be replaced with prerecorded or synthesized bass lines if no room is present for a bass rig. A nice 4-by-10-inch cabinet and matching head are the minimum requirements for large stages.
Stage microphones are necessary to amplify vocals at a concert. You will need one microphone for the lead singer and as many microphones as there are backup singers as well. Without them, it would be impossible to hear the vocals over the amplifiers and drums. In a live setting, all of the instruments are miked as well to compete with the vocal amplification. This way, all of the musicians and singers can monitor the sound on the stage for a good performance.