Grocery shopping should always be planned.
Don't just walk into a store, stroll around, and take what you think you might need.
You'll rake up a big bill in a hurry!
Make a list and by all means, stick to it.
Making a list will also save you time. You'll know what you need, and you won't be wandering aimlessly.
How to make sure your list is complete?
I have a master list. Just before I go grocery shopping, I'll go down my master list and write down what I need.
The master list has everything I've ever bought. In other words, it has everything I can possibly need.