That happened to me many times during last year, because my work now is split between Italy and China. The average layover is 5 hours, so I have plenty of time to read and program!
The most important discoveries were definitely Net::Server and Net::Server::Mail, they transformed some daunting tasks into a real programming pleasure!
Next modules on my list are Attribute::Handlers, Params::Validate and Config::General::Validate.
The second discovery was a bookshop in the center of Beijing, where I buy O'Reilly books that are useful after my laptop battery runs out: they are so cheap that I tend to read even topics not related to my job (ie. AI for Game Developers).