As a Villa fan living in Charlton I should be able to help with pubs. There aren't that many very close to the ground.
First thing though - it looks there aren't any trains from London Bridge on Saturday, which is a pain. You'll need to get the tube (Jubilee line) to North Greenwich then a bus or taxi or walk (at least 30 mins walk).
Given that, the best pub might be the Pilot which is not far from the tube station. Decent pub, good outdoor space. Still a bit of a walk to the ground from there, or a bus.
I'll be going to the River Ale House in East Greenwich, at least 6 interesting beers on tap, and some nice Charlton fans. Small so hope it doesn't get totally mobbed by Villa fans. About 25 mins walk to the ground.
Other options:
Closest to the ground is the Antigallican, just by Charlton Station - bit basic, possibly home fans only.
Hope and Anchor is on the river - used to be the away pub years ago. Should be decent there.
Rose of Denmark, slightly back towards Greenwich is ok, home fans only for league games, not sure about this one.
The Angerstein, about 15 mins walk from the ground is a Millwall pub. Not sure if they will welcome a load of Villa.
You could go further into Greenwich - Hardy's, Cutty Sark - but not very practical if the trains aren't working.
