You can get portable bottle warmers
I just give it to him at room temperature . Didn’t realise if that wasn’t ok
(In other words I don’t heat it after leaving the house )
If you are at a cafe you can ask for a mug of boiling water and put the bag woth breastmilj inside to warm.
I don't, just give it at room temp. It's fine out of the fridge for 6 hours
https://www.babydocshop.ie/products/tommee-tippee-on-the-go-bottle-warmer?variant=47854680277333&utm_source=google&utm_medium=cpc&utm_campaign=MB%20-%20P%20Max%20-%20Index%20and%20Over%20Index&utm_id=21502397230&gad_source=1&gbraid=0AAAAABMTjozOJGmI0vUhYUlf2cIOaA_b-&gclid=CjwKCAiA3Na5BhAZEiwAzrfagBjQkE36BVyv-o9AxyOhknBeINbuCUO_sfQBgY2IWM36p79UVhKR-xoCE4gQAvD_BwE