Data validation to keep a prefix

I am creating a budget tracker that will have a couple of cells for miscillaneous spend. The information in these cells has to start z.1 Furniture, z.2 Racking etc.

I would like to allow people to specify what the item is by typing in the cell e.g. if i had a budget for cuddly toys i would want them to type into the cell Z.3 Cuddly Toy

What im trying to get round to saying is that is there a way that i can use data validation on a specific cell so that any information typed in that celll has z.x at the start.

Many thanks,

Chemist