Choose from list to fill in a cell
 

I am working on a schedule. Our schedule changes often and I am trying to
simplify things.
I have the schedule with Location A & B, Monday thru Sunday, AM and PM
Shifts (total of 28 cells).
I would like to click in a cell, have a pop up box (or something) show up
and be able to choose names from a list of names and have their employee ID
show in the selected cell. Usually there will be upto 7 names on a shift in
one location at one time. I would like it to be displayed like "1234, 5678,
9012, 3456"

Any help will be greatly appreciated.