That is a good question. There are three approaches… the DAC/Headphone amp / closed back speakers… or get a DAP and closed headphones… they look like a thick iphone but are dedicated to music. In general this can be a a very good and portable. I have a very good one… and it sounds great. I have had dozens of DACs , and headphone amps, and headphones over the years. You can see my headphone system under my UserID. I’m not suggesting you go their.
Alternatively,the third way you could go is noice cancelling / blue tooth headphones like Bose Quiet Comfort… Sony and Sennheiser make them as well. This may seem sacrilegious because they are not high end. But, noise is the Emily of high end. Ever with closed headphones the sound is so compromised. I have had a dozen of rigs for travel and noisy environments. In my opinion a waste of time and money. Noise cancelling headphones are generally retuned to sound really pleasant when used with noise cancellation. The sound is a bit cartoonish… but designed to be really pleasing… in environments where all the important high frequency gets truncated.
I use my audiophile hat when choosing dedicated equipment in quiet environments. But when in noisy ones I slap on my Bose Quiet Comfort 30s and enjoy the quiet and lack of wires. I can walk anywhere… out the door. Gardening… traveling.
Hauling around DACs, headphone amps… wires…. A pain. I put on my Sennheiser 800s or Focal Utopia when it is quiet with my 30 lb headphone amp. Or go the DAP route they can operate wired or unwired. I have the top of the line A&K.