Tricky! I only host 15 with plenty of notice and with a bullet prof plan. To regularly do it with no warning would test me!
I think in some ways it depends whether you view it as ‘hosting a lunch’ or simply more people joining you for a regular family meal. By this I mean when I host I tend to go bigger on side dishes and have more variety, whereas with family it may be more simple.
Being prepared to cater for numbers is dependent on having a good store cupboard and freezer and recipes that utilise these.
Those part baked baguettes, rolls, ciabatta’s are good for impromptu hosting and have a relatively long shelf life. You can then knock together a quick lunch with the baguettes and fillings. You can also get gf ones.
I usually have tuna and sweetcorn
Cheese (often several varieties)
Cream cheese
Eggs
Often some form of cooked meats such as ham
Chicken breasts in the freezer.
I usually also have a well stocked salad drawer to add as sandwich fillings or as a side dish and every condiment known to man kind! As well as an impressive collection of pickled veg!
For a hot meal there is always a bag of pasta (for you gf), rice, cous cous in the cupboard, along with chopped tomatoes, various beans and pulses lots of herbs and spices etc so a tuna pasta bake, pasta arabiata, a Veggie curry or chilli. Always onions and garlic in the house too.
Eggs
Jackets are always easy for a crowd although do take a bit longer to cook.
A packet of good sausages, salmon fillets and chicken breasts in the freezer also really versatile
And a pack of puff pastry for quick cheese straws, sausage rolls, pies and tarts.