I've used the Radioshack speakers for well over 15 years: they are small, extremely durable and easily carried in a pocket.
Even with tons of use, I've found the required 9V battery will last for several months. If you plan to use your set-up abroad on short holidays, one battery should be all you need (worth bearing in mind given that 9V are not necessarily so easy to find). I carry spares with me as I typically go abroad for 3-5 months, but often still find that I don't need a replacement.
One thing you do need to carry with you, however, is a small screwdriver, which is the only way to easily take the back off and change the battery. Using another suitable object to unscrew the back will eventually "screw the screw"!
As an aside, I've found the 3G nano iPods, at least, to be much worse as playback devices compared to "classics". My two classics have "crashed" once (between them) in a total of three years use, whereas the nano has been consistently problematic over the same period. My local Mac store knew nothing about any increased risk in "freezing" with nanos, so maybe I've just been unlucky.
If you do have problems with an iPod, take it into a Mac store if you can. They replaced my problematic nano with a brand-new one for £35 (which was particularly good given that I bought the other one second-hand). Just for the record, the classics I bought were second-hand too.