How do I do this?

Ik this sounds stupid but I just HATE sharing my food. Like I bought it and I didn't want you to have any. In my house, people tend to take some of my food when I order then leave me with like a quarter of what I originally had. Anyways, I want to order some food without anybody knowing. How would I do so? I'm old enough to pay and such but I don't want to share! They always complain when I don't give them any so what do I do?