Blog's the stuff for work,
Blog's the stuff for play,
Blog's the stuff, when you feel rough,
to chase the blues away
--The March of Slime, Cytricon, 1955
Blog is the traditional drink served (although not always drunk), at the lowest class of SF fandom conventions. It is something like the Pan Galactic Gargle Blaster, except less appealing. It is sufficiently alcoholic to induce you to eat crottled greeps, but the LD50 is lower than that of Nuclear Fizz.
Blog was first advertised in 1955, when a mob of crazed SF fans (the Liverpool Science Fiction Society, to be exact) put on a 'Tapera' (taped space opera) called 'The March of Slime'. Blog was the official sponsor of the tapera, and flyers were distributed and banners were hung. It wasn't long before people started showing up at the hotel bar asking for blog; the nonplused bartender resorted to telling the disappointed customers (both fannish and mundane) that he was "all out, next shipment in tomorrow". Of course, there was no shipment, and the bartender finally resorted to mixing cider with rum. Of course, the real fans has already tasted blog, and were not fooled.
The 'real' recipe for making blog has long been a matter of debate. The original blog was reported to be made by Peter Hamilton with a brandy and egg flip base, and uncertain amounts of black currant puree, Alka-Seltzer, and Beecham's powder. For obvious reasons, this recipe is not universally accepted. Modern recipes usually include equal parts alcohol and weird stuff, although the weird stuff is technically optional. It is common to add something active to the drink, weather it be Alka-seltzer or dry ice.
The word 'blog' was probably created spontaneously by a very drunken fan, but there is a possibility that it comes from a mock-advertisement that appeared in an article written by J.B. 'Beachcomber' Morton in the 1940s:
"Why is Sir Arthur looking so gloomy, Sir Harry?"
"Poor devil! It's like this, Sir George." Lowers voice "His capillaries, set end to end, wouldn't circle the earth more than once."
"Phugh! That's dreadful, Sir Harry. Poor blighter! Is there no hope?"
"Oh yes, Sir George: BLOGGO. A year ago my capillaries, set end to end, would barely have reached China. Today they would circle the earth three times. But where are you dashing off to, Sir George?"
"I'm going to buy some BLOGGO for Sir Arthur..."
Regardless of whether or not this was the inspiration for blog, it's darn good writing. It should be noted that this drink, while preceding the internet-type blogs by a good long while, are not in anyway connected to them, etymologically or otherwise.