For grips, you can tie together a bundle of chopsticks, then grip it like you are holding a baseball bat. Twist in both directions, over and over. You can do it while watching tv or otherwise relaxing.
I also like archery as a form of strength training. I rarely make it to the range to actually shoot, but I pull out my bows and practice drawing them while watching tv or hanging around. It develops the fingers that you use to pull, and the arms, shoulders, back, chest. Pull both right-and left-handed for equal development on both sides, don’t become lop-sided.