I start out with cider (ice in the cider) and keep a vintage decanter of sherry on hand for the sherry scenes. I absolutely love being "in" on the toast "To a delightful weekend in the country" with Uncle Monty, Withnail, and Marwood at Crow Crag! I even found some sherry glasses just like the one Uncle Monty drinks from during the toast. (Still on the hunt for that tall one with the etching that he uses for the "I'm preparing myself to forgive you" line...). If you look at my avatar, you'll see I've put myself in!
As for snacks, it's almost always home-popped popcorn shaken in a huge lidded bowl with copious amounts of parmesan cheese, salt, and cayenne pepper while the popcorn's still hot from the pot.