For guitar and bass, the choice is going to depend on the size and format of tuner that you prefer. For instance, if you want a stompbox model, check out the TU-3 Chromatic Pedal Tuner. This is one of the most popular stage tuners anywhere, and there are great reasons for that: it's durable, accurate and easy to slap onto your pedalboard alongside your favorite effects. You can turn up the brightness on the TU-3's LED meter to make it easy to read even in bright sunlight during outdoor gigs, and it's loaded with all kinds of functions to help you keep your guitar or bass flawlessly in tune.
Are you a brass or woodwind player? Tuning is just as important for you as it is for guitarists and bassists, so be sure to take a look at the Boss Chromatic Tuner for Brass & Wind Instruments. One of the best things about this tuner is the clip-on contact microphone which attaches directly to your instrument's bell to make sure it reads the notes as accurately as possible, so your tuning will always be spot-on.
No matter your level of experience, Boss tuners are accessories that you should absolutely consider keeping in your gig bag. A quick tuning check before you take the stage is always a great idea, and with their easy-to-read displays, these tuners allow you to tune up in seconds so you'll always know you sound great.