Pretty much all of America will carry the folllowing three items in some form:
1) key or keys (car, home, whatever)
2) money
3) ID

Only an ultralight hiker might choose to ditch the keys, but 2 and 3 are highly recommended.

So once we get past that, the next three depend on where I am:

When I'm around home:
1) Cell phone
2) Flashlight
3) Multitool

When I'm "out there":
1) Flashlight
2) Multitool (oh I have so many now)
3) DR designed PSK Check out those great reviews!

When I'm on a plane:
1) Cell phone
2) Flashlight
3) Crappy Swisskey

I actually always have the crappy swisskey on me because its on my keychain, but, if I could only pick 3 it would not be on the first 2 lists.

It should be noted that I am assuming that any reasonable person will be carrying your ID and some money in a useful form no matter what/where they are going.