For excersise, I found that squats and calf raises (near) daily are extremely important when stuck inside. They engage your feet, legs, buttocks and core if I do them correctly. They are excellent exercises to do even in a top floor apartment. I feel much better when I do them regularly.
Also, stretch! I keep thinking back to all the stretches I learned in elementary school. I mean yoga is great and all. But, those generic stretches work wonders from sitting all day.
I also walk, but not as often as I would like. Neighborhood walks are good for mental and physical health. I walk when I feel stressed or tense and it helps me feel better.
For activities, I want to play video games or watch tv when I am bored. They are easy and don't cause me pain to do. But, I feel better if I make a to-do list of things I need to do and projects I want to do eventually. That way I can slowly work through the list inbetween mindless activities.
Also, reading and writing. These activities do not hurt, unless one has a migraine. Reading and writing engage the brain and make me feel productive. As do other hobbies like photography, drawing, painting, building mechanical objects or repairing old items. Accomplishing something makes me feel like I did something productive and so even working on a project feels good.
Stress is still an issue. I mean, have y'all seen the news lately? I have listened to so much calming music lately. Instrumental music that is usually in a major key and as slow as 70 bmp is perfect. If you do not like the calming music on youtube, try Bach, Brahms, Beethoven, or Handel.
Lastly, get outside or look outside everyday. This is important. There are birds and trees and flowers. The seasons are slowly changing. Nature is beautiful. And, I need my vitamin D. Eating healthy and getting the right vitamins are helpful for a good immune system.