+1 for Grumps and Darrell
I put on music I DON'T know and play along with it (various Pandora 'new jazz' stations on shuffle). Improvise over the changes cold without knowing where they're going. Try to get the melody down before the end of the song. Pandora has a replay feature for most songs so you can do it again
Standards are pretty easy, because they tend to go to the same places and you can usually anticipate where something is going to go even if you don't know the tune (hence the old adage "hum a few bars and I'll fake it"). Modern stuff is more challenging, especially Robert Glasper, Alfa Mist, etc. Lots of non-standard progressions, multiple modulations within a measure, etc. Anticipating changes in new modern stuff doesn't work so well, so you have to really listen and feel your way through. It's actually pretty fun.
My ears and fingers are MUCH faster than my brain. In fact, the less I think about it, the better it is. You have to be present in the moment and move with the music almost like interpretive dancing;not thinking about where you're putting your foot, it just goes where it needs to be. If you try to think about what chord/key/scale/mode etc you're in, and then think of what to play, you're already behind.
That's the best, most useful from a 'playing-with-people' type of ear training for me. And it's fun!!