The quickest way to do that is to use the selector tool, highlight a selection that you have done, use the field calculator to put in a 'key' value (ie week1, week 2 etc).
In any event, you are going to have to draw the boundary. If you had to reuse this boundary, then you could produce the boundary layer, then do a select by attribute or spatial join.
If you need them as separate files, then use the Split layer tool if you and advance license... or since you are using an old arcmap Split Layer By Attribute works for all license levels