You don't need breathalysers, there's no punishment for not having them.
Stick the headlamp converter stickers in the glove box in case you get stopped, but otherwise leave them off unless you plan on doing a lot of driving at night.
Hi-vis MUST be in the cabin with you.
Ramps will be fine, they're used to low cars and unless yours is 2mm off the floor it won't be an issue.
No GB sticker needed if you have it on your numberplate.
And yeah, they'll sell them at the port at a massively inflated rate Go to Halfords tonight, it'll be fractionally cheaper at least.