A tip from a past life working a customer service / food service job:

Learn a few words in a variety of languages. They are great conversation starters / expanders – I made a lot of actual friendships by talking to people (after taking their orders), asking them where they’re from, and then knowing a few words in their language. Nothing makes people happier than hearing someone speak their native language, no matter how poorly.

This was in a university town, so knowing a couple words in Chinese, Arabic, Hindi, etc. was useful.