| Well, Monkey itself is about as portable as it comes. Everything's self-contained and all required paths are local. The big problems come from the tools needed to build the translated source. For HTML5 (And Flash, I'm pretty sure), you're 100% portable. 'MServer' versions are available for all three major operating systems, and they come with Monkey. The only part that isn't contained in your Monkey installation is the build folder. Well, besides your source code and assets, anyway. Those can be placed anywhere you want.|
What you're probably talking about is using the GLFW target, or something similar. This is also completely portable (When done right). You've got a few options: You could install MinGW in a sub-folder, and change the path to it via "config.winnt.txt". For Linux and OS X, you'll need to use something like apt-get, or otherwise find an appropriate distribution. I haven't messed with OS X in a couple of years, so I can't really help there. I know 'C++ Tool' builds are GCC, though. You may need XCode for GLFW. Linux is as simple as it gets, though; just install GCC and run.
It all really depends on what you're using. If you want to deploy to Android, for example, you'll need appropriate drivers and SDKs. At the end of the day, GLFW and HTML5 should work with little hassle. If you don't want to store certain tools with Monkey, or with a relative path, you could always install the tools on each machine, and have your installation reflect that. Jungle would also need to be installed separately if you intend to use it. Although, your settings could be synchronized on Windows if you opt into it. Plus, it's not like a one-time setup is all that big of a deal. Just keep your source code and assets (And/or your Monkey installation) on the flash drive, and set the path up with your IDE (Jungle).
Monkey's actually a decent bit more portable than some toolchains, so I don't see the issue. Sure, it's not quite Blitz-level of portable, at least not without bundling MinGW, or using HTML5. Still, there's very little that wouldn't work with this.
I recommend installing your SDKs on the machines you use, then keeping the software you right on a flash drive, DropBox, or wherever you want to put it. The same generally goes for Monkey as well.