Feeding cat just biscuits?

My cat lived to 15 on dry food only. I always bought a complete food, but not always the same one, as cats do tend to get bored. I always bought whatever was on special, and mixed the flavours, and she was quite happy. As for the begging, it is in an animals interest to get food whenever they can, as instinct tells them that they don't know where the next meal is coming from (even though you could set your watch by them knowing when feeding time is!!). A little bit of tuna, or plain chicken as a treat would be fine.