You are leaving your house for the day, and 10 minutes away you realized you forgot something, what would you have to go back for, and what could you live without for the day?

Just wondering, yesterday forgot my cell phone and lived the whole day without it.
If it had been my wallet I would have had to return for it.
Had it been my bagged lunch in the fridge, I would have said to heck with it and bought a lunch.
With things you take when you leave, what would you have to go back for?