Pickholder - Provided your bridge saddles are close enough together...
Always have a few picks on top of the amp as well, & some backup spares in that little pocket in your jeans.
Tuning to the Mains
In the UK the electricity supply is 50Hz, in the US it's 60 Hz. Finding something with mains hum isn't usually very hard.
Bottom G is 49Hz, Bb is 58.27Hz & B is 61.74Hz... so... if you're in the UK, tune your G a tad sharp & in the US you have a choice - sharpen your Bb a touch or flatten your B a bit. Close enough for Rock 'n' Roll.
Pete.