I ran across this tip today at TheExcelAddict.com site – Open A Specific Workbook Every Time Excel Starts. It shows how you can set up Excel to automatically open all the spreadsheet files in a particular folder when you start Excel. Here’s how that works…
In my Documents folder on my C: drive, I created a folder called ExcelFileOpenAtStartup. In that folder, I have three spreadsheet files that I want to have open up automatically every time I launch Excel:

To set that up, I go to File > Options > Advanced, and in the General section I have the At startup option. I copied the link to the start-up folder I created in the above step, and then click OK:

Now when I open Excel, those three spreadsheets open automatically!

This is a great feature for someone who has a group of spreadsheets that they use every day, and they want to have them open up without trying to find each one individually.
I recommend checking out the link to this tip at TheExcelAddict.com for a few other tweaks you can make to this setup, such as putting file shortcuts in the Startup folder so that you can have spreadsheets stored in different areas still open up automatically without moving them to a new location.
TheExcelAddict.com also has a newsletter you can sign up for to get tips like these on a regular basis. I highly recommend it!