Most mornings I start with a few stretches and exercises.
The tennis ball is an absolute favorite of mine for stretching out sore muscles and tendons in tight and hard-to-get places. I'll probably make a video in the near future showing how I use it.
I also love therabands and small hand weights. These are easy, small items to keep at home or in the studio. That way one can get a few exercises in in between paintings!