As a multi-instrumentalist, I have had the opportunity to perform in several musicals such as “Singing in the Rain”, “42nd Street”, “Hairspray”, “Cabaret”, “Honk”, “West Side Story”, “Sideshow”, “Bye Bye Birdie”, among others. Because I am a Woodwind Player, my emphasis will be on woodwinds; I am not really in a place to describe the brass, string, or rhythm section books since I have not ever played out of them.
As a reed player, if your goal is to perform as part of a pit orchestra, I have found that it is absolutely essential to be able to double. There is a set of standard doubles for each of the saxophones, and they go as I am about to list them. Musicals tend to have 2 or 3 reed books, alto and bari, alto and tenor, or tenor, alto and bari.
If you are an alto player, you typically play out of the Reed 1 book. Usual doubles are flute, clarinet, piccolo, and soprano saxophone. Sometimes you even have to play Eb clarinet. This book is usually the most difficult and demanding. It also has more clarinet and flute parts than any of the other books. There is very little, if any, saxophone in the book unless it is a more contemporary, jazzy musical such as Chicago. This book also has the most solos and exposed passages.
This is the tenor saxophone player’s book. This book requires doubling on clarinet, flute, oboe, English horn, and occasionally piccolo. This book is mostly clarinet and usually doubles, and has harmony to most of the Reed 1 book.
The baritone saxophone player usually gets to play this book. The doubles include baritone saxophone, bassoon, clarinet, bass clarinet, and rarely flute. When there is no Reed 3 book, the Reed 2 player usually has to play tenor saxophone, baritone saxophone, clarinet, bass clarinet, and flute.
If you are looking to perform in musicals, but have not yet had the opportunity, I would suggest going to local shows and poking around backstage. You may run across an opportunity to audition for the next show. Usually musicians in the shows are regular, but are always looking for subs. It is tedious doing shows for long periods of time, so having a sub is always nice. If you are a student, you can always ask for lessons from the saxophonist in the pit so you are known, and if you get good enough, he/she could ask you to fill in for him a couple of shows.
If you are in high school or college, schools do musicals almost every semester. Churches also do musicals, so check with your local church. These musicals are usually performed with a prerecorded CD as opposed to a live band. If you are willing to volunteer for a musical and do it for free, you can ask the director to rent the pit orchestra books and you can put together a group that meets the instrumentation. Even though you are doing it without pay, you have the opportunity to impress the director who may use you for outside stuff that will pay, or you get good experience for the future.
One thing to know about musicals is the time that they require. The rehearsals are intense, and the performances never seem to end. By the end, even though you did not act in it, you know all the words to all the songs, and most of the dialogue in between. The only way you forget it is when the next musical rolls around and you have those new songs to get stuck in your head; you are no longer singing “All that Jazz” but “Oklahoma”. No matter what way you go about playing in a musical, it is a great experience and great practice on your doubles.