Load your vehicles up with food and water. Bring plenty for you and others. Fill your packs with it and break bread with others.
FOOD is the secret to great turnout at any event. Food means you can party for a LONG time! Eating food together UNITES people as a family!
Proteins and fats are critical, and carbs will help those not used to walking all day keep going.
Clean water is super important too.
Armies march on their stomach!
A solid day pack with handy things should be on everyone's back.
Poncho in case it rains, basic first aid kit, flashlight or head lamp for after hours if needed. food (duh), goggles for your peepers, small towel, small pop up umbrella, any meds that might come in handy.
You might could include a few small hand held defensive weapons, but the legality of those can vary, but with the nation on the line, legalities might just have to be overlooked.
All of that stuff should not weigh you down and will keep you in the game a good long time, hell, bring a spare for someone who might not have thought ahead.
hand warmers out the ass