"Newbie" where to start?!

[DollyDayScream]

In light of Brexit and Bill Gates saying something about the next pandemic killing 33 million, I'm seriously thinking about prepping (secretly - I don't want to be a laughing stock - BUT he who laughs last...).

What do you think a beginners box of essentials are?

It's best to think about realistic likely problems and realistic solutions. And then building in some resilience in your home so that you aren't as reliant on other people feeding you, keeping you warm and keeping the lights on. That is generally "the grid" of utilities and shops.
Realistically it is impossible to suddenly start relying on yourself for all of that, nor is it that desirable.
For me, the first realistic and likely obstacle is winter (no, not Brexit). I live in an ordinary suburb but sometimes the power goes out and/or we get snowed in. It may not last more than a couple of days but I have to put my mind to making that tolerable.
With Brexit, I think there will be an interrupted food supply followed by things getting expensive.
Take it from there.

Check out Sutton's Daze on YouTube- it is National Preparedness Month in the US and she is posting a video every day on different topics. It's American so there will be phrases and terms that you don't get straight away. However, she seems like a sensible and ordinary kind of woman who dials down the drama. Homesteading rather than prepping is a concept you might find less scary. There's a really nice UK homesteader/small holder Liz Zorab who also has a YouTube channel.
Autumn is actually a really cool time to start learning how to preserve fruits and veg - just have a go at making some jam to get yourself started.
Don't go mad and spend loads.
Prepper Pot Pourri is another channel to watch. She's a middle aged woman from Michigan that all the other noisy gun totin' male US preppers respect.

You could also look at building a "Go bag" or "Bug out bag" - you need to leave home at short notice and stay away for 72 hours. What would you need in that bag? I say "build" because it's personal to you. There's a lot of tactical types on YouTube making it seem like a pseudomilitary thing. Again, interesting and useful ideas but don't try to be something you are not.

In terms of Brexit, as well as essentials, I'd also have a think about things you might need but may no longer be available - either at all, or on demand but would affect your quality of life if you could not get them. For example, things you need for hobbies.

As an example, if you have a child who swims, I'd make sure I had at least one spare pair of goggles or if they do ballet buy the next size up of ballet shoes now.

I always assume we are likely to be staying put where we are.

I would start with a stock of food to last you for a week. Think about what you would all actually eat and put that aside so for example jars of pesto and bags of pasta and tins of sweetcorn and beans rather than assuming you'll suddenly want to eat jars of pickled herrings and aubergines in oil. The major benefit of this is that it isn't wasted cost. If everything is sorted out and there are no issues then you can just use up the food you'd put aside.

Then build up from there. Think about fuel, medicines, vitamins and other essentials and work your way out to longer periods.

If you have the space then plant things now that will help you next year and put aside some seeds to enable you to keep supplementing your diet from your garden as the seasons change. Fast growing stuff like perpetual spinach can really help to supplement a restricted diet.