How many uniforms for a kindergartener?

For those who have/have had children in schools which use uniforms, do you
have any suggestions on how and what to buy? DD will be required to actually
wear the full school uniform for parochial school K in the fall (instead of
the "clothing that adheres to the dress code" that pre-K is allowed), and
I'm considering going ahead and buying a few pieces at a time, a size up,
since I KNOW what the uniform policy is and it's unlikely to change (I think
there would be a rebellion, given the number of hand me down loops and
multi-child families which already exist).

Thanks!