If you shop separately from your roommates, you don't always know what food is off limits — and what's up for grabs. A simple sticker system clears everything up, and ensures your roommates don't eat your food. Image from xalionmalik.
Over at The Kitchn, hermitonthehill explains how they use this system in their home:
We had a handy sticker system for food items in the house. Dollar store dot stickers, each person had their own colour, and a green dot meant HELP YOURSELF. This way any pantry or fridge items were not confused and you could share any left overs or over stocks.
Most people can remember what they bought, so you probably don't need to label your own food, but this is a quick way to show your roommates what you don't mind sharing. Make things even easier by using big dot stickers (like this pack of $2 ones from Woolworths) that can be seen with a quick glance.