I admire your guts :)
Other people have offered good advice.
We've sponsored people in the past. I would say one of the main things is providing the sponsor with what's been agreed, e.g. a an after show report within x days. The sponsors are running a business and handing over hard earned...
I've done the taking my lorry to move horses who where about to be flooded out. That was a tad wet and stressful, but they were all saved so happy days.
I will check with the YOs of the current horses as to what their plans are should the worst happen.
Make sure you're happy with the way the gearbox works, some go the opposite way to that which you might be used to.
One friend used to used an airbed instead of a normal mattress. She took it out when not staying away, said it stopped it going mouldy.
Spares of everything:
stirrups and leathers
hairnet and bobbles
And generally found to be useful stuff:
food (biscuits, pot noodles)
decent water container
pens (including permanant marker)
basic grooming kit
Two Rotties and a GSD, so not really an issue. The fact that they'd all merely lick and ask for tummy tickles is academic. Admittedly I only walk two of them at a time, but any combination is likely to keep folk at bay from just a looks POV.