Well I may sound nuts but as with you guys we have also fretted about this.
We actually set up a "trust fund" for our dogs (we make small bi-weekly contributions via payroll deduction).
While we haven't figured out the "who" yet, we did want to make sure that whoever does in the event, that they aren't burdened with expenses and cannot bear the financial burden.
You can actually set up this type of trust with a financial advisor. Ours is set so that expenses have to be at a vet, groomer, or from a pet store (food).
Just in case someone went nuts and decided to use the money for a tv or something. I don't think anyone we trusted enough with our babies would do something like that, but, I am a bit cynical and figured it was the best way to go with the funds.
It's not huge, but we have been at it for few years and it should cover enough food for about 4 years and routine vet visits for 4.
We still contribute to it and would like to have enough to cover at least one or two large procedures should they ever arise.
or maybe we are just nerds.