Go for a 15 minute walk after lunch. A post-meal walk has been shown to reduce blood glucose by up to 35%. It's a simple, free way to improve afternoon energy levels and help with digestion, mental clarity, and creativity.
Use the photo memories feature on your phone to stay in touch with people. Look at it each week and send the photos to the people who pop up in them. It always prompts a quick catch up with people from your life and gives you a low-friction way to regularly stay in touch with old friends.
When you're learning something new, spend 5 minutes trying to teach it to someone. Make a note of where the other person gets confused. You'll get an immediate sense for your level of understanding of the topic and where you need to dig in more.
Think and journal on bigger picture questions about your life, direction, and daily actions. Ask yourself this: If you were the main character in a movie of your life, what would the audience be screaming at you right now?