One time I was interacting with a stranger (so long ago, I dont remember who. Possibly just a store clerk). At the end of the interaction they looked me in the eye and said 'Have a great day'. It took me off guard, but made me feel really good in a way I couldnt put my finger on. I now say the same thing to everybody I meet in my day, in the hope I can bring somebody else that same feeling and genuinely make them have a good day.