A good 1/4″ cable and a backup cable
If you play electric guitar or acoustic electric guitar you want a good cable that will carry you through the gig with a clean sound. Plus another one just in case or if someone else forgets their cable!
An extra set of strings
In case you break a strang!
A good tuner
Most folks seem to be using the type that you place on the head and it tunes by vibration. This is the quickest way to tune between songs.
A good metronome
To practice with. I recommend the metrotuner because it tunes too.
Cordoba guitar
Great bargain on a spanish acoustic electric guitar!
Picks
I always like to have extras around.
Sandpaper
If you play with your nails, sandpaper is a cheap way to keep them smooth.
Cloth to clean guitar
Amp
My favorite is the Fender HotRod Deluxe. It has overdrive and spring reverb. And it’s a tube amp. Very versatile from Wes Montgomery to heavy metal.
Battery-powered amp
If you want an acoustic amp, the crate battery-powered amp works well.
Surge protector
Highly recommended to protect your gear and your health.
Gig bag
I like the patagonia bag because of the compartments, the ability to use it as a backpack. The money back guarantee.
Amp cover
Protect your amp from rain, cold and minor bumps and scratches.
Ipod
To listen to music on the road
Headphones
Ditto
Recording device
To record with
Shakers
Nice to have some percussion
Beatcraft
To have beats to play with
Transcribe
To transcribe music