I usually bring a "donut" type bed for my cats - they like the coziness and security of it, especially when they are new to shows. I also bring a piece of soft material, rug, etc. to line the floor of the cage with. I haven't used tents in the benching cages, but I occasionally see people with small ones. Bring one along and see how it works.
However, when you get to the show, there are probably going to be lots of vendors - selling everything from beds, "show toys", grooming supplies, treats and everything under the sun! I usually come home with at least a few things and I am sure you will too!
A lot of people showing more than one cat often use corner shelves and/or hammocks in the cages so the cats aren't right on top of each other. I'm sure the vendors will be selling them!
Being that it is your first show, if you haven't already, call the entry clerk and ask them if they can bench (seat) you next to an experienced exhibitor who is willing to help a new person. It will make your first experience that much more enjoyable for both you and your babies.
Which association are you showing in? Are both of your cats Birmans? Good luck and have fun