Whenever I travel with a job, they make sure I have prenty of free time to do whatever I want.

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You should not incur any additional expenses if you agree to travel with them, unless they are optional. Therefore, they should cover all your basic meal costs. The only exception should be if they get you a hotel suite with a kitchenette, and you can do your own cooking.

In my experience:
They pay you for any hours worked, OT if necessary.
They pay any travel expenses (airline tickets, train, etc.)
They pay for any meals you have with them. However, if you have the day off, you pay for your meals.

An additional bonus either per night or lump sum is sometimes given, since you'll be away from home/passing up on babysitting jobs, etc)

Some things you might want to consider, depending on where they are going:
will you have a vehicle to get around on your time off? Will you have a key to the room/house? (Seems obvious, but once I wasn't given a key!)

My employers want me to go with them on vacation and provide care during my normal working hours. Should I only expect my normal pay or should I be paid an additional fee? Not sure what is appropriate here. And no, we don't have a vacation provision in our contract.