When you benefit from receiving help from a mentor, coworker, or boss, take a few minutes to send them a thank-you email or write them a handwritten note.
While you, as an employee, may feel entitled to an annual raise and not feel like you need to say thank you, remember that a raise is only guaranteed if written into your employment contract.
One reason to consider writing a thank you note is because the boss, another teammate, or an assistant put in the time and effort to organize the lunch. And the company likely picked up the tab.
You can also use the message to inform people of your last day. Optionally, you can include your contact information at the end of your message if you want to stay in touch if you are moving to a different company.
Your message can feel more generic than when you want to thank someone for something specific. But, of course, if you have something recent you can specifically mention, be sure to mention it in your note.