I had a little battery powered Bluetooth speaker that also had a 3.5mm "Line In" jack. I foolishly expected that to work with the audio out jack on the Pi. But it didn't and I learned quickly that the details of Linux audio are arcane and nasty. So I just bought an earphone plug speaker from Radio Shack for $20. The Auvio brand rechargeable unit works fine for my purposes -- and has a builtin volume dial.
To go with it, I downloaded the "festival" text-to-speech software. It's crude but ok in a 1980s sort of way.