Warm-up exercises: set up a personal warm-up routine program, or have it drawn up by your expert guitar teacher.
Warm-up exercises can range from scales, modes, some technical exercises, chords, certain songs, … up to and including stretching exercises. Start this with little pressure on the fingers and build it up. Make a small program of about 15 minutes. Yes I know, this is nice in theory but not always possible in terms of timing … Sometimes it’s unpacking and stage without warming up. But see previous point, provide in the playlist a kind of warm-up song for all musicians! Ditto : a vocalist will NEVER open a gig with the technically toughest and most difficult songs.
I myself have a squeeze dumbbell and Gripmaster for muscle toning and warming for the fingers and hands, and an expander for the shoulders and elbows. The squeeze dumbbell and Gripmaster are also very useful while you are in the car, for example, on the way to a gig, or if you are waiting before you go on stage. Please note, never use too heavy a load as this is very harmful to your joints and muscles. As a warm-up, it is best to use soft, light but certainly no more than a medium! Those things don’t cost a lot of money, but anyway, health always comes first and you don’t save on that! You can buy these items in any fitness store and often also from a physiotherapist.