How can I open 4 files with one click?

I have
- my budget in one file (one sheet per year)
- my taxforecast / -returns in one file (one file per year)
- my salaryslip in one file (one file per year / raise :)
- my investment scheme in one file

All of these have referrals or links (don't know english term) between them.
e.g. both tax and budget files picks the monthly salary from the salary file.

Any ideas as how to open the (4) files with just one click?
I would prefer a method that allows me to have the same order (file 1, file
2, ..) every time.