I have been trying to remember how/what I equipped my nephew with when he went to DC on a school sponsored field trip. What they were allowed to carry was severely restricted due to their ages: 12-14 years of age.

I had him take the following in a PSK:

55 gal trashbag
a blanket/small pillow
a roll of quarters
a signal whistle
a signal mirror
2 MRE's
a pre-paid VISA card ($50.00, I think)
a map of Washington, DC
cell phone w/chargers (ac&dc)
empty water bottle w/water purification tablets inside

In his wallet:

Insurance card
Military I.D.
Name, address, & phone number of his 3rd cousin who lives in Md

That's to the best of my memory.