One thing I do when I am feeling sad is....
I tend to over think it sometimes.. So when im really mad i just play a game on my phone and try to stay silent
Learn about botany, or just sit outside and stare at my plants.
Pet the kitty and try to talk to someone
I take a long shower :)
I take a mini nap, or i take a long shower while sitting in the bathtub contemplating life
Reading, writing or watch videos
I love listening to music. If I'm sad I make a cup of tea and listen to music. I also tell myself that it's perfectly fine to take a minute to rest while I do that.Self care is productive and necessary! Especially if you're feeling blue 
Listening to music, watching Netflix/favorite movie, chatting to my mom
Beat myself up for past mistakes.
Listen to music, and cry
or reading sad stories and cry