A few months ago, my college-age daughter, while vacationing out-of-state,was held up at night and surrendered her wallet. It got me thinking: Wouldn't it nice to have a wad of spare cash on my keyring? Even if I never get robbed, there are times when spare cash would be handy. I may lose my wallet. I may forget it or leave it at my desk. I may run short of cash till payday. As I explored what's out there, I found that most solutions are repurposed pill-fob tubes; most can hold just a single bill, and nearly are so short that the bill must first be folded. These restrictions wouldn't do! A U.S. $20 bill won't go far, and if you would need to use the emergency bill to buy a train ticket, the machines won't take a bill full of creases. And trust me, if you ask strangers, "Would you be so kind as to trade me an unfolded $20 for this one?" most will suspect that you're offering a counterfit. I also discovered that these tubes are listed under a wide range of names. A sampling: bill cache, cache vial, emergency bill holder, pillfob, pill fob, pill vial, pill keyring holder, keyring tube--you get the idea. A U.S. bill measures 66mm (2.61 in.) wide by 156mm (6.1 in.) long. I wasted a good bit of change buying pill tubes advertised as 70mm or 75mm before realizing that this figure was for the outside dimension--or worse, included the keyring lug. First I tried the Original Pill Fob from the Herringtoncatalog.com. A pricey stainless-steel affair, this was overkill. It also proved too short to hold a bill unfolded and too narrow to hold more than one. I ended up buying four pill tubes and one toothpick holder. From left to right: silver "Large Key Chain Pill Fob Survival Kit Container" from U.S. eBay seller ferrocium; also sold as "Water Proof JUMBO Aluminum Pill Holder Key FOB / I.D." from U.S. eBay seller emeraldviz. green "Pill Cache Container box case bo Keyring holder VIAL" from eBay seller bid-store, located in Asia. It also comes in blue and red. I favored green to remind me there's money inside. black "Aluminum Waterproof Bunker Capsule / Pill Fob" from the U.S. dealer goinggear.com. green "Water Proof Long Aluminum Pill Holder Key FOB ID Holder" from U.S. eBay seller emeraldviz"]emeraldviz[/URL]. Many colors are available. toothpick holder #2500 "jungle camouflage" from Hart Woodcrafts in the USA. Here are the five tubes shown alongside an unfolded U.S. $20 bill. As you can probably tell, there's no way for the bill to fit into the middle three tubes without being folded: If the tube's inner length is shorter than about 70mm, you'll have to fold the bill. To insert two or more bills, be sure to interfold it (nest the folds), as shown with this $20 and $10; if you fold both bills along the same side, one end of the roll of bills will be thicker than the other, wasting precious millimeters of inner diameter: So how much do they hold? From left to right: 6 bills, no folding necessary 3 bills, interfolded; maybe 4; unfortunately, a 16340 lithium cell got lodged inside before I could test. 4 bills, interfolded 2 bills, interfolded 1 bill, no folding necessary...but you must tape a grab tab" or you'll need tweezers to extract it from the toothpick holder's constricted neck. Here are the five tubes in different order, showing how the bills look when you peer straight down into the tube: I chose the big, fat silver tube. I can't tell you how secure I feel, knowing that come what may, if I have my keys, I have two $20s, one $10, two $5s, and one $1...all usable in a ticket machine.