I'm guessing you're envisioning an urban situation.

Personally, I dislike much bulk where the hidden pocket is designed to ride, so my first goal would be to keep it "slim and light." Besides, to do otherwise would possibly compromise the "hidden" feature, and increase likelihood of detection by a would-be robber.

• $60 cash (3 x $20)
• Debit card or credit card
• Prepaid calling card
• List with important phone numbers
• Photon Freedom microlight
• Couple of aspirin (if just robbed, gonna need 'em)
• One day's worth of prescription meds (if applicable)stored in aspirin tin or foil
• Spare car key (not a bulky 'original issue' with embedded electronics, but a flat, bare-bones version)

If I was traveling internationally, the list would change.