I use rattle can paint quite often. I found an easy and practical way to shake the cans without aggrevating my tennis elbow.
Cut a piece of 3" schedule 40 pvc pipe 10.5" inches long. Insert an Oatey 3" test plug in one end and tighten. The Oatey test plug came with a wing nut I replaced with a regular nut.
Take an old Tee shirt and cut a square out of the back.
Wrap the Tee shirt around the can and stuff the can and Tee shirt into the pvc pipe seating the can at the bottom.
Attach a drill to the Oatey bolt on the test plug. Set drill for high speed. Hold can in tube upright and spin for a few minutes.
I found this idea somewhere in the folds of the internet so I cannot give credit to whoever thought this up.
Works great just keep open end of pvc up to keep can from being ejected.
I bought an acrylic small bottle shaker but this would work just as well if not better and cheaper for mixing acrylic paint.