This is a subject of our life that comes with mystery here I will give you options and pointers so you can give the right message to the right person.
A lunch date may be tricky, this is because is on day time. Maybe that is a little complicated, or maybe it doesn't have to be!
Here are some examples:
A simple dress can be used on day time or night time, with the right accessories
May be the little coat with help this day time look be more fresh while other color might help make it into a night out outfit.
Very simple, yet casual, comfy, and chic.
So! Jeans : are allowed
Don't wear heavy jewelry
Don't wear heavy makeup ( nobody likes a cakey face )
Dress casual yet feminine.