You can be able to send multiple attachments as one file in an email by ensuring that the Flash is installed in the service you are using. You select attach and then find and highlight all the files that you want to add. The next step is to hold down the Ctrl or command option and then hold down the shift key and click open. You can go to, http://email.about.com/od/yahoomailtip1/qt/How_to_Send_an_Attachment_with_Yahoo_Mail.htm, for more reference.
Install winZip or any other zipping program, put all the files you need into one folder and compress this folder into a zip file. This file can be sent by email and be opened by the recipient if he/she has any zipping program installed.