Some options I can think of:
- Exercising.
- Baking, or cooking a tasty, healthy meal for yourself and/or others.
- Listening to favorite music, podcasts, or audiobooks.
- Doing a random act of kindness, or honestly complimenting someone.
- Talking with a friend or family member.
- Going to a park to play on the playground, to hike, to geocache, or to sit and enjoy nature.
- Making and savoring a favorite cup of tea or cocoa.
- Meditating (Here's a free 28-day guided meditation course for February, registration still open. I'm in no way affiliated with the site or the company nor am I making or promoting any purchases.)
- Creating and using a 'Happy List': When you feel emotionally stable, make a list of things that make you feel better. Keep it in easy reach so when you feel bad you don't have to think, just read and do. Some possibilities — 7-minute workout, make a favorite cup of tea or cocoa, meditate. Here's an example.
- Working on an existing hobby (without buying anything new); singing or playing an instrument.
- Napping and sleeping enough at night.
- Indulging in a tiny treat, such as a morsel of exquisite chocolate.
- Going for a walk alone, or with a pet or loved one.
- Taking a shower or bath, maybe with bubble bath, incense, or candles.
- Using a homemade skin scrub or mask.
- Painting your nails, finding a new style for your hair, flossing, etc.
- Learning something new on sites such as KhanAcademy or DuoLingo.
- Writing letters and/or sending packages to other people -- and receiving them.
- Taking a 'free' unplanned, unscheduled day.
- Volunteering.
- Read books you own, or borrow some from the library.
- Going for a scenic drive, bike ride, or transit ride.
- Journaling or writing.
- Trading massages with a loved one.
- Local free or Pay What You Can days at theaters, zoos, and art, history, or science museums.