You should make a list of items to look for and what the latest "completed sales" prices were on ebay. I only look for ebay sales that had multiple bids on ebay. Its a good idea to bring cash. Hopefully most vendors will accept cash.
Figure out how much you would possibly spend in your wildest dreams and then double that number. Bring the cash in a mixture of 5, 10, 20, and 100s. If you can offer correct cash then the sale goes so much quicker. If your interests are specific, then it is not a problem to walk the entire show on Thursday. If you stop and look at everything from prewar to 2017 items, Lionel to MTH to Flyer to ?? then you will need the whole three days.
Bring an extra pair of shoes and something to cover your purchases with when you drop them off in your car. The sun shining through the cellophane on a warm day can affect some products.
I like to eat a good breakfast and have snacks and a cooler with drinks in my car. Then I can take a short break in between bldgs and eat a snack. As far as I know water fountains are only in the blue/silver bldg and the orange bldg.
Look at the map on the eastern division webpage and print it out for a reference of the bldg locations. There are usually two shuttles that run in a circle amongst the bldgs. It can save a lot of wear on your shoes. Bring a sturdy shopping bag for your purchases. Pack a cheap poncho in the car in case it rains.
The orange and purple hall have mostly dealers and the most newer equipment. The red, white, silver and blue is mostly used but some new (or new old stock also).
Seriously bring lots of cash, more than you ever think you will need. You can always put it back in the bank when you get home.
If you see what you really want and the price is fair, then buy it and don't look back or think about it any more. Just cross that off your list and move on to the next item on your list. If you pause or walk around the corner, etc. to think about it, there is a high probability it will not be there when you come back. I have read many stories about that on this forum and a couple of experiences myself. The angst of paying a little higher price fades very quickly as you get home and enjoy your new found prize. However the regret of failing to buy an item lingers in your mind for a very long time.
It will be an awesome experience. The Eastern Division and their invaluable volunteers put on the greatest show imaginable in the O scale kingdom.