I recently got Bose QuietComfort 15 Acoustic Noise Cancelling Headphones.
I had previously tried passive earplugs and headphones that claimed 30 dB noise reduction, and got little value out of them.
The noise cancelling headphones suppress a good deal more train (BART) noise, enough that I’m now able to read nonfiction while on the train.
It won’t help with the situations where noise bothers me most (multiple conversations nearby) because it mainly eliminates predictable noises. It makes speech sound more distant without affecting the speech volume a lot. But reducing the cost of train and plane travel is valuable enough that I feel foolish about not having tried them earlier.