
We used to have a cat like that, she regularly went missing for 2-3 days, we found out someone up the road thought she was a stray and was feeding her and letting her sleep in the house. We found that the cats normal routine was to sleep over night in our house have breakfast, stroll down the road for a mid morning snack, stay at the other house till about 5 have some food then back to ours ready for us to get home have her tea and then sleep.
This went on for about 6 - 8 months without us knowing until the vet told us she was getting too fat so my younger brother followed her to find out where she was getting all the extra food from :D