LlamaLAN

I've never had a prob with this, but I know it caused a ruckass at the last LAN event. Before I cart off my PC I start up each game while I'm connected, and then I switch off steam, unplug the network cable, and restart Steam in offline mode. It seems to do the job and every game will start, but I haven't made absolutely sure by connecting to a LAN server.

What's the official line on what someone does to be sure they can startup their games on a LAN?

Exactly as above, LG and I both did the same ...

update Steam
run each game
(join a server) - although it shouldn't be necessary
shut down Steam/shut down your machine
unplug from the network
start up your machine
allow Steam to start in offline mode
re-run each game to be sure that the process as worked
DO NOT reconnect to the network (make sure it is the last thing you do before you pack down for the LAN)

Ideally you should do this 24 hours before the LAN since that is the last time that the organisers will have been able to update their machines including the dedicated servers.

CD

I do something similar,
I dont let Steam through my firewall
by default, so I let it update etc
then stop-restart and refuse it access
to the 'net - works just as well.