How can I stay fit without going to a gym?

Go out walking or jogging. Swimming. Take up a sport. Have a treadmill or exercise bike in your house.

Doing yoga, meditation, walking daily in every early mornings & evenings

Do light exercise like doing house chores or hobby or controlling your diet daily...

Yoga is best for you.

Get a mini trampoline. A good quality rebounder has a zillion advantages. Google ans see nasa studies . Invest in hand weights. 

Have a healthy diet and go for a morning walk.do some useful exercise at home for 15 to 20mints.

Go for a walk in your neighborhood every day

1. Drink water in copper vessel early morning.

2. Doing Yoga at Home  

3. Take bath after 15 minutes of performing Yoga. It will elevates your mood.

4. Food and nutritional part.

Exercise at home.  Push-ups, situps, light weights,  crunches,  walks,  hikes, biking,  etc.

1 hour of Exercise = physical activity. 

you will not be able to stay fit without a form of exercise