When I do long events I have learned to do a few things.
1. Adjust my sleep schedule so that by the time I would normally be getting tired the sun is already up.
2. Take a shower before you go to bed the day before, have everything packed and ready to go (in your car already if you feel comfortable with that), including laying out clothes shoes. This allows you to wake up go to the bathroom and get out the door right away.
3. Eat, eat, eat. This is very important, if you keep eating every few hours you'll have more energy to keep going. Don't eat crap, eat something with nutritional value. I like Protein bars for breakfast and snacks. Take a real lunch break, get some more good food in you. Take 5 minutes to eat a bar every few hours. Take a real dinner break, again eat good food.
4. Drink lots of water, you don't want to crash because you were drinking soda/energy drinks. You will be going to the bathroom a lot, but that's okay.
5. Take any time not alloted for food where you don't have something to do and take a 20 minute
nap if you can, otherwise just sit down.
6. If you don't need to stand, then don't! Standing uses more energy than sitting or laying down.
7. If you have time, and possibility of, depending on the
venue, take a shower.
8. If you are in a space with temperature control, turn the heat up a little
bit. You are looking for that temperature range that is too annoying to sleep in buy not so hot that your sweating profusely due to the heat.
9. If you need a break take one. Simple as that, better off sleeping for an hour or two while your not directly needed (they will wake you if it's that important), than dragging your body around all day and losing focus.
10. Talk to your employer about getting more
venue time to spread out the hours an extra day next time (in my expierience this has actually worked).