I've left my two cats alone, for up to 12 days. I just put out tons of food, and an extra litter box. And they were FINE.
As far as my dog, I could never BEAR to kennel him(it'd kill him I think, he's such a spoiled baby). I even tried leaving him with my friend once, who he loves! Nope. He cried all night(even though he was in their bed!). I had to cut that weekend getaway back to the first night only.
So, since then, I've only taken vacations that are dog friendly. He's been to TN like 20 times, and FL once. And I can only go during the cooler months. It's too hot for him to stay in the car more than a couple of minutes, during May-Sept.
Dogs are great. This will be my last one. I'm sticking to cats from here on out(I LOVE to travel).