Can't really add too much more to whats already been mentioned. I second the st austell brewery tour, although you want to get in and out of St Awful as quickly as you can....
If you make it to St Agnes there's a lovely pub down near the beach called the Driftwood Spars which has a brewery across the road, they do decent food and usually good beer.
Falmouth is good for pubs, though I haven't been since Covid.
Skinners brewery tour, then few beers in the old ale house in truro, just opposite there's a shop called the red elephant which sells beer from all over but they stock just about all Cornish breweries beer. I think verdant stuff sells out pretty quickly though. Opens at 11am.
I can't think what it's called but in Constantine (nr Helston) there's a shop which apparently has just about any kind of spirit you could think of, not sure what the beer selection is like though.
I don't often buy canned beer but if you do then obviously Verdant and Pipeline (new st agnes brewery) sell hoppy IPA type canned beer. There's a couple of breweries in Ponsanooth, dynamite valley and treen. Dynamite valley do decent beer and have a brew pub type thing. There's also Woodmans wild Ales, beer made out of stuff he forages near Ponsanooth. Keltek brewery in deadruth do decent beer, generally more esb/bitter than ipa's, their new(ish) porter is decent.
If i think of anymore i'll add later.
Mind the pitchfork waving locals while your down.