How do I assign a single Keystroke to multiple items?

A macro program like autohotkey is what you're looking for.

Since skyrim has a consolified interface, almost any action can be done with keystrokes alone.

The trick is to use the favorites menu, and walk trough it while selecting the things you want.

A macro I have for example is:

• q opens quick menu

• wwwwwwwwwwww moves to top of list (number of items in list.)

• eseequips or unequips an unrelated weapon and shield

• the desired weapon is has a known state (unequiped)

• sse moves to wapon and equips it.

• ssse moves to shield and equips it.

• q closes quick menu.

It isn't instant or very quick, but it saves a lot of time.

However, this setup is fragile and basically only works when all items of the Quick menu have consistent names.

Unfortunatly there is no way to do it yet. Like @Fambida wrote, lets pray for a mod that bethesda does not banish.