Have been going to Fan Expo for the past 3 years now, I think it's safe to say...the first time you go is always the best experience. I felt super exhausted and drained getting to/from the north and south buildings. They definitely added a bit more to their line up and made the show a bit beefier this year.
Make sure when you go:
-you bring lots of snacks and water. Food is expensive inside and not always to your liking. There is food options outside so make sure you do your research/make reservations.
-Wear comfortable shoes/clothes, I know if you're cosplaying that will be a tough one.
-Bring LOTS of cash. You never know what you might see and it's always best to be safe then sorry...or at least avoid ATM lines/charges.
-Bring plastic covers/folders for your photo op/picture signings to go into. There's no point in buying at the show...there aren't a lot of stands selling them.
-Bring your charger/external batteries. You don't know who you might see wandering the expo and you want to make sure your devices are charged.
-Bring a backpack/big bag to carry any shopping you do or free stuff you get.
-Make sure you have your ttc fare/or book hotels early.
-HAND SANITIZER. This is a MUST.
-Napkins too.
-Buy any photo ops you want online or ahead of time. The line ups are crazy and you don't want to miss your photo op because of that.
-Plan out your day(s) with the master schedule they offer online. Print and highlight.
-Give yourself about 20 mins to get from one building to the other.
-Make sure you make a meeting spot in case anyone in your group gets lost, there isn't a lot of service inside certain areas of the buildings. So it's best to meet somewhere instead of calling.
-For the parents, make sure you pack everything for your child. A blanket for them to sit on when they're tired and lots of water/snacks for them.
I think that's about all I can think of, it's what I think is pretty important from my experience going to Fan Expo.
I hope you find it helpful! Good luck and enjoy when you go!