Any tips for a future mommy who will be 5 months along come GenCon?

I think an alien chestburster costume would be pretty awesome for someone who's pregnant. 

Other than that, I have no advice. :) 

First of all, congratulations!

Take care of yourself. It's easy to get tired out from all the walking and standing you're going to be doing.

Don't worry about not being able to see everything... GenCon is so big and diverse that it's impossible to do everything you might want to. Personally, I have a goal of playing two events per day, one in the morning or afternoon, and one in the evening. After three straight days of that, I'm really exhausted on Sunday, both physically and mentally. So scale that back -- if you do one cool thing a day, you're ahead of the game.

Also, make sure you get enough water. The air in the convention center and hotels will be cool and dry.
 

Congrats.
Depends on your level of activity at Gencon. 
If you are going to game, there should be places to sit and keep off your feet.
If you like to walk around, have comfortable shoes.

• Make sure you have access to plenty of water.  I'd bring a refillable water bottle-I believe there are water stations to refill.
  
• Bring some food that you can carry with you, the wait lines for nearby food (including food trucks) can be insane.
  
• Scout out areas that you can go to to put your feet up.
  
• Tums might be good to have with you.
  
• Don't be shy- if you are not feeling well. Say, "I'm pregnant and need to sit down."
  

Thanks for the congrats. :)

Thankfully this will be my 6th Gencon so I know the lay of the land pretty well. And was already planning to not set foot in ICC on Saturday.
Been trying for years, anyone bumps the belly and I won't be held responsible for the elbows that will be thrown. ;)

Now, off to work on a chest burster costume... 

I am also going to be pregnant this year. I will be 7 monthes. My doctor told me to drink plenty of water and wear comfy shoes. 

I second the recommendation for comfey shoes.

And that idea of an alien with chest burster costume is awesome!

Food!  I was 8 months pregnant last year for our first Gencon and my husband learned quickly to feed me regularly or I got really growly.  I would lose track of time and then he and our friend would try to go to the food trucks - looong lines, long wait times, and hungry pregnant lady was not a good mix.  Make sure you are eating every couple hours.

Bring extra dice. You're critting for two now.