For contests requiring an overnite at a hotel ,I used to bring my converter along with my charger .The morning of the contest, I used to get up early to charge. No more.
Now I get to the field an hour or so before the contest, connect the charger to my vehicle battery and hangout. Unless you are planning to squeeze in practice flights before the meet, the vehicle battery will do them (depending upon size and # of charger ports) in roughly 30 min for 4S 2700 and 40 min for 4S 3900 @ 1C. Put in more juice; time reduced. I personally do not like charging batteries more than 5 hours prior to use. Of course, no danger to even 8 hours before BUT the longer the battery has to keep the full charge, the worse it is for it in terms of longevity ( # of cycles realized). As a practice, I also put them into storage as quickly as possible after a flight. Don't wait until the next day.
One more thing- I don't go overboard with using my vehicle battery. If required ,I start the vehicle and run it for 15 min.