Excel - Concatenate range

Not as pretty as a custom function, but gets the job done.
To concatenate all values in range A2:A100, place the following formula into B2 and drag/fill it down to B100.

=CONCATENATE(B1,",",A2)

If you want to concatenate all values in a range on the condition that there's a 1 in column B:

=IF(B2=1,CONCATENATE(C1,",",A2),C1)

To avoid the , or 0 at the beginning, in the first cell that should have a value, enter the value manually and copy the formula to the cell below it.