There are probably some towels with loops on in my mother's wardrobe. 
Food: you could read the hell is ever closer threads. Lots of advice on there pre October 31st.
Think breakfast dinner, tea and snacks. Drinks.
Toiletries, cleaning stuff, laundry, washing up.
Pet food, pet supplies
Medications.
Storage wise: between us we use: under the stairs, under kitchen units behind kick boards, top/ bottom of wardrobes, top of cupboards, under beds and sofas, behind the sofa, under the dining room table, behind the bath panel, in the loft, behind books on the bookshelf.
There is a comprehensive list of Brexit stash items, but getting the essentials first.
Think what you could substitute for fresh items, Eg tinned fruit and veg?
What your family will actually eat. No good buying 20 kilos dried pasta if no-one eats it.
Think about food that is easy to prepare if you are feeling shit or limited power/water. (Eg we have occasionally had to turn water off to other flats when work needed to be done on the stop tap. )