I'd recommend a JBL Clip 2:
It's bluetooth (though it has a wired connection too) and that creates some advantages for playback use. It also has a carabiner, which is useful either for hanging it to a branch or from your belt straps. It has good battery life, is waterproof, is fairly loud with pretty good sound, compact and light and isn't very expensive. It pretty much ticks every box for a playback speaker.