A quid is a slang term for the British pound. So currently, 1000 quid (or 1000 pounds) is about $1500 US dollars.
Sidebar is a theme feature introduced with Version 2.2. It's basically a vertical column provided by a theme for displaying information other than the main content of the web page. Themes usually provide at least one sidebar at the left or right of the content.
Sidecar is a term bartenders use for the leftover liquor they pour into shot glasses, which is more likely where the cocktail got its name (although how or why I'm not sure... still more believable than the motorcycle theory, though).