I think the dress underscores Brown's view of himself as more than a mere digger, maybe not a full fledged archeologist, but someone who hass a greater level of expertise than a digger.
That's very possible. Overall I think it's accurate of the period, you can see it in Greece as well in old photos around that time, suit tie and hat (ALWAYS HAT outdoors), any kind of writing job, small stall vendors, greengrocers. Hell I recall farmers wearing a shirt and jacket to the fields when I was little and that's not too long ago. Academics too would go
I just recalled Nikolai Vavilov, one of history's greatest botanists, sadly being brought down by bonkers socialist ideology, and Trofim Lysenko's ambition (can read his story
here, the villain Lysenko's agricultural policies resulted in famine and millions of deaths), he travelled to do research in some of Russia's most inhospitable places wearing a three-piece suit.
As for his tobacco, I'd wager he smoked his village tobacconist's own blend, nothing fancy, nothing named. All too possible to be something similar to Gawith's stuff, after all it's real working class tobacco at heart, nevermind what we've made it to be nowadays. Ropes for miners to chew for example in lieu of smoking in a pit, plugs for sailors etc. Interesting fact, the British Parliament still has a
snuff box for use by MPs. I doubt many use it, but it's fun that it is there!