Yamaha makes a Uke body packable guitar now on sale at Guitar Center...$100 or so.

As a pro musician (teach, and in a working band) all the talk about unwanted jams/noise is warranted but probably not necessary. Few people on this forum need to be told to not pollute (noise, air, etc.). If I bring instruments with me, it's either because I'm with other musicians, was requested too, or am by myself. The OP requested packable instrument suggestions...give the guy some credit to know where to play them.