I usually prefer just using my credit and ATM cards when I travel, since it tends to give the best rates, is available pretty much in any country in the world (with a few exceptions, like Iran), and is much safer than bringing cash. However, in some countries in this world, you actually get a better rate exchanging cash, usually USD. For this reason, on a long trip spanning many months, I needed to find a way to carry large amounts (several thousand) of USD. What I ended up doing was simply keeping them in an envelope in a secret pocket in my pants... for pretty much the entire time I was traveling.
I've had break-ins before in my hotel room, so I don't trust leaving stuff there. I also find it a hassle to use the hotel "safe" since in many cheaper guesthouses that I stay, that means leaving it with the front desk which often takes a long time (they have different procedures where they sometimes wrap your belongings in tape and have you sign the tape, or need you to take every 100 USD banknote out to write down the serial number etc), and I don't like the idea of the sometimes shady front desk staff knowing that I'm carrying several thousand USD.
And so, I carried this envelope next to my skin for a couple of months, and this is what it looked like by the time I reached Ethiopia. It lasted about one more month before disintegrating completely (going through rain and sun and whatnot) and I had to upgrade to a new envelope :)
Note: For most travel, don't bring large amounts of cash, just bring your credit or ATM cards instead. There were special circumstances, and particular countries I visited that made it useful for me to bring all this cash.