You can do more than just have a good day or a reason for a good day.
If you don't tell someone else, if you don't try to help others have a good day, you may not be doing enough.
I'll bet that at some point during the day you will have the opportunity to tell someone that you are having a good day and why. Take that opportunity and spread a little goodness. I believe that it will make both parties have an even better day.
The effort is little, the pay-off is huge. Make today better, today's a good day.