Start with the basics. Grab a notebook and pen and start an inventory.
First walk through the entire house and spend some time in each room thinking about all the tasks that are performed there. Write down all the tasks that are performed, and generally how often (Daily, weekly, monthly, rarely). Make sure to include tasks that all family members perform, not just the ones involved in making a list.
After all the tasks are written down, go through the rooms again, and write down all the items that are used doing these tasks, especially but not limited to the consumables. Make sure even the lesser rooms like closets, bathrooms, laundry rooms and garages are included.
Next decide which of the tasks are essential, needs, and wants. Essentials tasks are those that are necessary for life to continue: Eating, drinking, going the bathroom, etc. Needs are those that would be necessary for health and safety: Bathing, washing dishes, etc. Wants are things other than Essentials and Needs.
Next spend some time thinking about what all was written down, and as life continues over the following weeks, go back and make additions or changes to the list as necessary.
Use this inventory to help understand what items around the home are critical and what consumables are most important.