The first thing you need to do is think about what you are prepping for.
If it's just general everyday uk type disasters, like leaves on the track/snow etc... bringing the country to it's knees for a couple of days, then you are prepping to stay at home for a few days with perhaps a power cut/water cut/shops empty of food.
If it's SHTF, then you might be looking at prepping to bug out i.e. leave the house for somewhere else.
For the bugging in option, you start with looking at what you would need to get through 3 days.
3 days food, 3 days heat, 3 days drinking/cooking/cleaning water, 3 days lighting, 3 days medication if required by someone in your household, 3 days cash in case the cash machines don't work.
So, you buy enough food to get you through 3 days & store it, store enough bottled water @ approx. 6 litres per person per day + ideally have a water butt in the garden you can use for toilet flushing, make sure you have torches & batteries/candles enough to make it through 3 days, get a £10 camping stove & half a dozen bottles of gas when they are on sale at the end of the summer or a Kelly Kettle (runs on twigs) so you can make hot water/hot food.
A packet of baby wipes or a facecloth (one per person) & small bowl of water along with some hair refresher/dry shampoo will go a long way to helping you feel cleaner in the short term if you can't take a bath or shower.
If you have kids or adults who use the tv or tablets for entertainment, you might want to consider some battery banks & a small solar charger for them so they can recharge/run their tablets to keep them entertained for at least some of the 3 days too.
If it's winter, a couple of hot water bottles should keep you warm if you have blankets, or you can get more fancy with a calor gas heater/wood burning stove set up, budget & ability to have a wood burning stove dependant.
That is your basics covered for 3 days even if you have a power cut, lose your water & your heating at the same time whilst all the shops are empty.
Once you have 3 days, you build it up to 7 days, read a lot then decide how seriously you intend to prep & how long you think you should have supplies for.
Longer term than that, unless you are going to start buying in stocks from Mountain Supplies (dehydrated 25 year shelf life very expensive option) & have your own well, you can't just buy the solution, you need to learn skills to obtain/grow/store food, water etc...
Bugging out, you need bug out bags for everyone in the family, a secondary location to bug out to & a full on prepping forum where you will find endless bugging out lists of things you need to do/learn up to & including forging your own tools.
Those kind of preppers usually also keep bug out bags in their cars including things like those petrol handwarmers etc.. in case they get snowed in whilst in a car.