Put dry ice at the bottom of your cooler to prevent the rest of your ice from melting.
Buy a tin foil pan if you need to bring a lot of food or meat. When you're done it can be simply thrown out instead of cleaned.
If you don't have tickets to the event and can watch it on TV, go tailgating anyways and bring a generator and TV!
If you don't have a generator you can buy a power converter to plug into your car. Remember to bring jumper cables too.
IsItDoneYet.gov offers advice and recommendations for judging when various meats are finished cooking.
Hot cider, hot chocolate, a little Baileys Irish Cream all go a long way in keeping you warm in the cold.
Bring a bit of styrofoam padding for your feet during cold weather events.
Try to do most of the prep work before leaving. Examples include making the burgers and marinating the meat.
Do something to uniquely identify your drink so others don't drink it: partially crush your beer can, have an odd color cup, use a marker, etc.
Always have an easy to set up canopy available in case it rains or it gets too hot.