Here's a simple formula to help you get started. Take the amount of food you would normally need to buy to feed your family for a day, multiply it by seven, and you'll have a week's supply. Every week (or every month if you're low on funds), try to buy food for another week. That depends on what you like to eat, as well as the choices you made in the first step.
First of all, you need to decide how big the storage stack you want to create. Right now, during this pandemic, they recommend a 14-day quarantine, so be prepared to stay at home for 2 weeks straight. However, if you're preparing for a possible loss of work, eating 1 to 2 months can be very beneficial. I have a family of 6, so I understand that storage can be expensive.
You want to feed your family, but you don't want to spend your entire budget to do it. If you take any prescription medications, it's a good idea to have a 30-day supply, if possible. The concern is that they may be scarce during emergencies, but if you need to isolate yourself, you may not have access to a pharmacy. I would start by getting organized and seeing what you have, what you need and making a list of things to supply me with.
In addition to guiding you through the meal planning process, there is information on how to stock up on your master list, how to create a restock list (with free printable templates) to help you rotate your stock and make sure it never runs out; and, most importantly to save money, how to create the list easiest pricing ever, which will help you store food at rock-bottom prices. Make a list of the ingredients you use regularly, then you can start slowly stocking up each week when you see good deals.