I know it’s a bit off topic, but curious to hear from others

I’m a HS teacher with 150 students. This year I got a fridge, micro and coffee maker in my room to make the days easier. I have a few students who repeatedly ask me for soda and water from my fridge. At first I said fine because I’m a pushover, but now the same are continually asking every day. It’s getting pricey and I Feel like they’re taking advantage. If they were impoverished or straight up hungry, I wouldn’t mind, but this is mainly just a matter of what I perceive to be greed/forgetting to bring their own.

Today was the final straw, a kid who is not even a student of mine came to my room to look for a friend. She saw my keurig and immediately demanded I make her a coffee when I was in the middle of teaching!!! I said no, I’m teaching right now. She returned 10 minutes later and asked again. Does the sign on my door say “Starbucks”??

I think I need to draw a hard line and start saying no.

How to say it nicely but firmly? Thanks.