Remove random customers and view impact on turnover and profit

I have approximately 20 customers occupying bins in a warehouse. They all occupy different quantities. The bin capacity in the warehouse is 500. The bin requirement by the customers is greater than 500 so I have to give notice to some customers. I would like to have a drop down-list with a check box next to each customer, so I can do random selections by checking different customers to see the impact of removing certain customers. For example, if I select customers 4, 7 and 11, I want to add the bins occupied by those 3 customers and deduct the bins for the 3 selected customers from the overall total to get closer to 500? My database has turnover and profit by customer so I will consider that impact as well. I was hoping to use a combo drop-down box with the ability to check different customers? I have attached a sample file.
Thanks in advance

I have found a solution by using check boxes next to each customer. I would like to create a list of the customers that have been checked but can't figure this out? I have attached a test file.
Thanks in advance

You could use the AutoFilter feature to select the customers and the SUBTOTAL function to total the values for the selected customers.

Excel Filters: Excel 2007 AutoFilter Basics

Sum Filtered List With SUBTOTAL

Thanks for your reply but AutoFilter is not the elegant solution I am looking for.

Once again, thank you for your response but I am not getting the correct customers with this formula?

Sorry. Should be this...

=IFERROR(INDEX($A$2:$A$10,SMALL(IF($C$2:$C$10,"",ROW($A$2:$A$10)-1),ROW(A1))),"")

Brilliant! Thanks very much.