It looks like you should be able to easily pull the cookies from your pcaps with Wireshark or tshark using filters based around HTTP Cookies.
You should be able to match against http.cookie as a string according to the filters protocol reference: http://www.wireshark.org/docs/dfref/h/http.html
Some more general information about filter syntax (including operators) is here:
http://wiki.wireshark.org/DisplayFilters
I'd fire up Wireshark on your pcap and use Find Packet with a known string and then use the right click menus to have Wireshark craft the filter for you (as described some in the manual section 6.2.2. Pop-up menu of the "Packet List" pane at http://www.wireshark.org/docs/wsug_html_chunked/ChWorkDisplayPopUpSection.html
You can then use that filter (copy and paste) in a console with tshark to rapidly search large pcaps or script the searches trivially.