Some airports have little "dog yards" - so you could take him outside. There are also ususally pee areas designated outside by baggage areas (for traveling dogs). So, you'd have to go back through security - but at least he could get out, stretch his legs.
I've taken my carrier INTO the bathroom, on the plane - to see if he wants to potty, drink water (do NOT give water from the plane's faucet though), take him out for a bit.
For flight travel, I bring: pee pads, baby wipes, extra towel, brush, extra dog food (in case of major delay), small treats, Nutrical, "hamster" water bottle, childrens benadryl, chew toy, pepto, id tags, harness, leash.....I THINK that's it.....
