How do I get my coworker to stop helping himself to my coffee (that I make daily in my coffee maker)?

I have been working in my present job about a year and a half (employer has been the same for over 15 years, but in this present department, 1½ years). When I came, and was given my own office, I brought a coffee maker and I make coffee every day. This is a great savings to me, instead of having to pay about $2 per day on the outside. Plus I like the convenience of being able to drink it for prolonged periods (I add a lot of milk to it and make 20 oz stretch into three cups that I will have until around 2 or 3 pm).

My coworker is a food grubber – in other words, if I have food, he comes looking for it. I don’t usually mind. I have my own supply so as not to burden others by asking for food. I am talking about snack food – I keep stuff that I might need so if I am hungry, I am independent.

With the coffee, I told him in the beginning if he wants to have some, to help himself. I did not mean to have it every day, and I would think a reasonable person would not take it every day, or if they did, they would reciprocate by buying some coffee for the hostess once in a while. Today he was out in the morning so I thought “let’s see if he picks up coffee when he’s out instead of having mine.” He came in and took my last cup.

I don’t want to start an argument with him but it’s starting to get annoying, since we’re at the point now where he’s taking one cup per day. Is there a way to tactfully tell him to either pick some up now and then or start making his own? He has his own coffee maker in his office, but apparently my free coffee is better! :)