The warmup exercise I give to every student

It's not rocket surgery...4 fingers - 4 frets. Not much brain power involved because you are simply "pressing buttons" which then lets you focus on your technique, posture, tone, dynamics, or anything else you may need to zoom in on.
You can also add in stretches by going beyond 4 frets ...more to come!
www.zakkjones.com
Other permutation examples...
2 4 1 3
4 3 1 2
1 3 4 2
3 1 4 2
4 1 3 2
2 1 3 4
3 4 2 1

[@alanbaral3546]

And, I'm so happy you still have that guitar. :)