What's the risk of static building up during the trip and zapping components through the IO ports?
Near zero.
I want to take a PC, pop it into a carry bag
Unless the bag and it's contents are a combination known to generate static (plastic bag, woollen contents?) you should be OK. PCs are often shipped by the manufacturer in a plastic bag.
If you are still worried and don't mind looking crazy, you could cover the IO ports. Maybe with tinfoil :)