No equipment at all. I would have to say push up and sit up. There are so many variations you can do.
Yoga is nice and again many forms of it or similar.
However, should you deicde to ponder outside, a park when I lived back in FL had a nice loop to it and as you run it there was pull, dip bars, bench with feet holders, monkey bars, and other various things off the loop.
I like chin ups and pull ups personally. If I could do what these guys do and the ripped/shredded part would be nice bonus.
This channel is pretty awesome. BarStarzz on YouTube.
A video of an old guy in pretty shape than me I am sure.
https://www.youtube.com/watch?v=kaoY6gumdYg