The Boy Scouts have it right...Be Prepared.
Don't wait till the night before the event or better yet...the DAY of the event to check your gear or weapons over to see if they are in working order or you are missing something!
Here are Several Aspects to keep in mind:
Most Events have defined Start and Stop times and even times of Missions. These are important to game play and enhance your experience. Coming Late can affect how the game is played or how others interact with you. Be prepared to sit out and wait if you come in the middle of a Time based Scenario.
Basic Equipment List - An Event will publish what is required for Game Play during the day. Items such as a Dead Rag, Signed Waiver, Watch, Radio, BIO BBs or uniform types are examples. If you show up without these specified items, it can affect the game experience for you or others during the day.
If you come with only one Battery for the day and it dies, Be Prepared to sit the games out. Bring several Batteries (if possible) and your charger. Some Events do have charging stations or electric power for charging your batteries, but not all. Same deal with Gas or CO2, bring enough to keep you going for the day. Most events do not have Gas or CO2 available, but some might have some for sale. Bringing a backup such as a Spring Shotgun is a good idea to allow you to keep playing if your Battery Dies or you run out of Gas/CO2.
Bring enough Ammo with you. Although some events might supply some BBs for you, bringing enough to start with will ensure constant game play. Some Events will Sell BBs, but I have found that I like certain Brands for my gun to ensure correct operation. If the B.E.L. requires BIO BBs and you have none, be prepared to sit the day out as some Fields will not let you play on them without them. They might have them for sale, but going to an event and having to buy BBs there can get expensive.
Guns Break. Guns Fail. It is the Nature of our Sport. Bringing a Backup Weapon to an Event is always a good idea (if you have one). A CO2 Pistol or Spring Shotgun can be a cheap backup weapon which can keep you in the game if your Primary Fails. If your Gun Breaks during a game and you do not have a backup, Be Prepared to be annoyed if you paid for the Event and now can't play.
Just some things to keep in mind the next time you head out to an Event or Open play.