When Spit Happens
1) Play a Quick Chord - Playing multiple holes is a great way to clear spit. If you can incorporate this spit-clearing chord in the music, even better.
2) Quick Aggressive Tap on Leg - When the harmonica makes a dead-stop on your leg the spit keeps traveling and clears the reed slot.
3A) If not a memorized solo, avoid the stuck hole in your improvisation.
3B) If a memorized solo, then look to another musician to solo. While they're soloing switch harps or work on clearing the jammed reed. When looking back to you when they're done with their solo, jump back into the chorus you were about to play when spit happened or jump ahead to the last chorus to finish the song.