One app I used quite often on the Pebble is a TOTP app, where I could retrieve my code from anywhere, even if I forgot my phone that day. Since the battery life was awesome, it was comforting knowing I wouldn't get locked out of my stuff easily.

I also used an app to see a camera preview from my phone and as a remote shutter, I also relied on NavMe to see the Google Maps direction while walking or while riding a bike.

Another app I was using was to send HTTP requests to toggle some of my IoT stuff, that was quite handy too.

IIRC the quick replies could be entirely customized, and I found myself using them quite often.