I'd highly recommend looking at the prepper threads. Loads of good advice and lateral thinking there.
Ideally try and get enough in to last you 2 weeks is the usual advice.
Off the top of my head:
Bread (but be flexible if you can't get your usual preferred sliced loaf remember to think outside the box and get things like wraps and rolls instead - and they can all be frozen too)
Milk - yes long life but also non-dairy subs can have long dates, dried can be fine for use in hot drinks, baking etc
Breakfast cereal - if your lot will eat porridge oats are cheap and go a long way
Preserves - obviously, by their nature last a long time
Hot drinks supplies - tea/coffee (whatever your preference is), sugar/sweetener if you take
Sandwich fillings - not fresh ingredients - I'm veggie so pretty limited here but sandwich spread, eggs last quite well. Omnis can of course also have tuna, tinned ham, pilchards, salmon, sardines, corned beef
"Stuff" on toast - baked beans, spaghetti of course but also tinned mac n cheese, ravioli, tomatoes, creamed mushrooms...
Crisps, nuts and other snacks like this have good long shelf lives
Cakes and biscuits same
Ok this stuff isn't the healthiest but unlikely to do much harm to have them for a short time.
Everyone going daft for pasta but remember rice, noodles, cous cous and...instant mash are all long life carbs too.
Remember most fruit and veg is available tinned too.
Dried fruit - again usually not ideal as high in sugar but for now very handy long life products containing vitamins and fibre!
Cold drinks - squash lasts ages and takes up less space than fizzy.
Toiletries - I think loo roll already thought of by most, hand wash too but remember normal basics like shower gel and toothpaste.
Hope that helps you get started