I grew up in an area where we were evacuated on a fairly regular basis, and I am afraid old habits die hard - evacuation is highly (highly) unlikely where I live now, but we have an emergency box for each cage of animals we own.
Our piggy evacuation box (we have 2 one for each piggy cage) contains:
8 C&C grids + cable ties (enough to make a 3 x 2 cage)
2 fleece blankets
2 bath towels
half a shower curtain
1 water bottle
1 zip lock bag of pellets
1 syringe and sachet of recovery food
1 fleece tunnel
I cardboard box
1 vacuum packed bag of hay
It really is the absolute bare minimum, and it is all stored in a small plastic tub underneath each cage.
We also have one pet carrier per cage, so in an emergency we would only need to take the carrier (with pigs inside) and the plastic tub with their supplies.
This would allow us to set up temporary accommodation for them wherever we ended up and give us enough food for at least 2 - 3 days.
I think this sort of thing is something everyone should have, becasue even if evacuation isn't an issue, in the event of a house fire we would follow the same protocol. I know you are not supposed to stop to get your pets, but depending on the situation, I would like to have that option.