I bought a tin of [human] cookies for my barn owners one year.
Depends on the relationship you have with the owners. Since you are the only boarder, maybe you are closer to them. But I figured just the "I thought of you" gift of cookies was enough for/from me.
The idea for doing something for the help is a good idea too. Even homemade cookies in cute baggies would be appreciated probably. (as long as they don't have allergies or something!) =P
Resturant gift certs are nice. Grocery store certs are even better.
However, the best gift you can give is a heartfelt thank you. Write your own card!