A site called SDR Traveller sells ultralight, strong, and discreet bags for traveling to places where such things are necessary. Their most eye-catching item is the 1M Hauly Heist, a bag designed to carry US$1 million in cash that also doubles as a Faraday cage for shielding your electronics from radio frequency tracking.
From the description on the page for the 1M Hauly (which holds the million bucks without the RF shielding):
In many countries project expenses and payroll for the local crew need to be carried in cash. Whether you’re managing a team of thirty working for months at the edge of the grid, or on a solo trip to negotiate a significant cash transaction, the 1M Hauly is designed for discreet, safe carry of up to $1 Million USD in strapped, new or used $100 USD banknotes.
Designed to address the six main issues with carrying significant volume banknotes in field: risk of discovery; risk of damage (especially in high-humidity, monsoon environments); container robustness; carryability; glide; and in-field accounting.
Note that $1 million in $100 bills weights 20.4lbs. The site also sells smaller money pouches (in $10k, $100k, and $400k carrying capacities) as well as a durable duffel. All the bags are made from Cuben Fiber, a material originally used for yacht sails that’s four times stronger than Kevlar at only half the weight. (via @craigmod)