I used this rig extensively while delivering pizza until 2006. You find a lot of freaking wireless networks when you deliver food for a living, since you eventually find your way to every single backroad and cul-de-sac. These days, I use a MacBook, 500mW Alfa adapter and Garmin GPS12, or a 300mW Prism PCMCIA card in my Jornada 720 PDA, both with high-quality external antennae.

Hardware:
NEC Versa 4050C Laptop (Pentium/90MHz, 4GB, 40MB)
Linksys WPC11v3 802.11b PCMCIA card
Garmin eTrex GPS with Power/Data combined cable
Vector 350W Inverter
Angle aluminum holds laptop in rear window (used to be bungee cords)
Software:
OpenBSD 3.5
XFree86-4 (640x480/16bpp)
BSD-Airtools for AP Logging, Packet Gathering, and WEP Cracking
Ethereal for sniffing
Links2-GUI for web and uploading logs
gAIM for messaging