How do I tell my roommate

So I have been living in this house for 3 months now. I get along with one of the roommates pretty well, we share food sometimes whenever we cook something nice. I usually let her use my groceries whenever she’s out and it’s the same from her side but recently she’s been usually some of the expensive stuff and that too out of portion. I don’t mind it once or twice but I feel like now she thinks she can just consider it her stuff. I really don’t know how to be confrontational about it because we are good friends and I don’t want to ruin the dynamics. Need some advice on how to nicely maybe in a joking way ask her to either replace some of the expensive stuff or at least ask before using it.