Oddly, I have heard there is a major campaign, but have seen almost nothing of it. I obviously don't read the right sources. (Yes, have seen bits on gov.uk.)
And, other than stocking up, it is actually difficult to know what to do to prepare.
Bake some Welsh cakes and get the babysham on ice.
It's going to be a Brexit party!
Fail to prepare prepare to fail at having a Brexit party.