WPA encrypts the radio transmission only between you machine and the WiFi router only. Once it exits the router and enters the establishment's ethernet network, it is in the clear, and someone could sniff the packets on that network if they had access. Anything you enter or receive in your browser or transmit as emails theoretically could be seen, unless you were on a secure socket layer page
If you are on a web page that use secure socket layer (HTTPS), then the communication of text between your browser and the web server is theoretically secure.
However, a nasty little trick that has been played on public WiFi connections is to hijack the DNS servers for that connection, and redirect certain addresses to spoof sites
Remember, anyone who controls a router (or a WiFi connection) can direct normal domain requests to any DNS server they wish. What thieves can do is to build a bogus DNS table that directs say Bank of America . com which would normally be 123.456.789.123 to 234.567.890.123 which is Phishing4Fun . hackers . com -- then they put a simulated BofA login page on the phishing website -complete with https - thus capturing your login.
This trick has been done by people on laptops who broadcast a 'open' WiFi at likely locations such as cafes -- people who use that 'public' connection then are funneled through the thief's laptop instead of the cafe's connection.
Now, whether someone can read what is on your computer or not depends entirely on what services you have open -- if you have file sharing and printer sharing and windows file sharing etc turned on, then they can see whatever you have allowed them to see.
They would not normally have access to your keychain
So turn off all services to the outside world, and turn on your firewall.