Being in tune with everyone else in the jam session is of the utmost importance!
Checking your tuning often is essential as environmental changes like heat and humidity can change your tuning over the course of a jam session as well as putting on and taking off a capo. There are a wide variety of tuners available. As a multi-instrumentalist, the D'Addario Micro Tuners are appealing because they are small and discreet while providing a consistent tuning experience across instruments. They also tune using the vibrations of the instrument so a noisey jam session doesn't interfere with tuning.
D'Addario Micro Guitar Tuner - For attaching to the headstock of various instruments - not just guitar.
D'Addario Micro Soundhole Tuner - For attaching inside the soundhole of most guitars.
D'Addario Micro Banjo Tuner - For attaching under the brackets of the banjo pot.
D'Addario Violin/Viola Micro Tuner - For attaching to the body of a fiddle.
D'Addario Eclipse Tuner - Great for multi-angles, especially on a dobro.
Snark Super Tight Tuner - Another great option for a variety of instruments.