Brilliant item available for sale from Shomer-Tec, producers of 'Law Enforcement and Military Equipment.'
The descriptive blurb is so good it deserves to be reproduced in full:
The "Brief Safe" is an innovative diversion safe that can secure your cash, documents, and other small valuables from inquisitive eyes and thieving hands, both at home and when you're traveling. Items can be hidden right under their noses with these specially-designed briefs which contain a fly-accessed 4" x 10" secret compartment with Velcro closure and "special markings" on the lower rear portion. Leave the "Brief Safe" in plain view in your laundry basket or washing machine at home, or in your suitcase in a hotel room - even the most hardened burgler or most curious snoop will "skid" to a screeching halt as soon as they see them. (Wouldn't you?) Made in USA. One size. Color: white (and brown). To add realistic smell, check out "Doo Drops" on Page 65.
Or, of course, you could just hide your money in an actual pair of dirty pants.