1)get a good hotel. for us it has made ALL THE DIFFERENCE IN THE WORLD. we are at the hilton garden inn. it is important that they be able to serve a good breakfast so your not wasting time in the morning before work looking for something to eat. it is also important that the hotel not be far from where you are working, that way you can spend time on the problems at hand and not on commuting.
2) bring a laptop. I know you may not have one, but scrounge like mad to get one before a trip. we have had trouble getting computer resources on site.
3)attempt to get VPN access. offsite all you realy need access to is email, and you can use xxx.com, but in a pinch its nice to have backup access to the system.
4) eat well. our longest day has been about 15 hours. eat good meals when you get a chance and you will last longer. we had steak for 3 people.. with tip cost $160.
5)last but not least.. DO ALL THE LEG WORK YOU CAN before you go. get well defined CTQ's and know EXACTLY what you are to be doing to be successful. don't get distracted from your goal. you can work on other things, but make sure that after your time you have attained your goal and have the data and product to prove it.
6)oh yeah.. one more thing. buy a GOOD paper map of the area in case you get lost. we got lost on our day off when we were out site seeing.