If you want to transfer all your reimbursables to an invoice, you can do so by hitting the button "Bill open reimbursables".
A dialog "Add open reimburs. expense" will open. Here you can decide what reimbursables to add to your invoice. Just check the appropriate. Reimbursables with a strikethrough dollar sign are not chargeable or have no retail prize. Those won't appear in your list for your invoice.
All reimbursables you checked will be transferred to the invoice. Please read the chapter Invoicing for further details.