I found a more convenient way to keep track of what I need to buy at the grocery store. Instead trying to remember what I need when I am about to head out the door (which will almost always result in forgotten items) or randomly writing things down on scraps of paper (which will certainly get lost) I started doing this:
I just write my shopping list directly on the fridge door with a whiteboard marker when I realize I am out of a certain item. Then, when it's time to go to the store I can write the list on a piece of paper and take it with me or take a picture on my phone and refer to that as I am shopping.
Once I have bought the items on my list just wipe off the old list and start a new one!