I can fit a Pi in my overnight bag, but I can't fit a monitor. How can I remote log into my Pi when I'm on the road? This is a Catch-22 — I need a network address (an IP address) to log in, but to get the address I need to be logged in.
A related question: I want to connect my Pi to a new WiFi network, but to connect I need to give the beast the network SSID and passphrase — and again I need to log in first...
There are several solutions to the first problem — one good one is to set up your Pi so that it blinks its IP address on the status LED. For the second problem there are also several solutions, including editing the WiFi config on another machine that has an SD card reader, or setting up access to your phone's WiFi hotspot.
I've written a Raspbian package called BlinkIP to do some of this stuff, and you can download it from our new Ubuntu-hosted package archive.
Happy networking :-)