I fly A LOT for projects and this is what I've learned from it all:
Carry on everything you possibly can. I actually leave my 442, 744t, wireless units, and shotgun mic (sans Rycote blimp) right in my Petrol bag and use that as one of my carry on items. I don't pack it in a case or anything. It's all right out there in the open for TSA to check, go through, and inspect. I have yet to have them ask me to power it on but I always have it available to power up if they do ask. It is a good idea to have a couple audio files loaded on just in case.
I bring with my Pelican 1650 case and put my miscellaneous items in it (blimp, short boom pole, sox, underwear, batteries, etc. I try to keep the weight under 50 pounds, which is tough because the case itself weighs 35 pounds empty. Anything else heavy like batteries, lead weights, etc I put in a carry on. Until they get fussy about carry on weight I suck it up and shoulder the extra pounds. Plus, I'm a cheap skate and I don't want to pay over-weight bag fees.
My second carry on is either a small bag for clothes or my laptop/additional audio gear bag. It all depends on how long I'm staying, what gear is needed for the shoot, if I'm footing the bill for all the travel, etc.
I basically figure that I want to keep with me at all times the essential, and expensive, pieces of gear that I'll need for a shoot. If the airline loses your bags it's easier to replace a boom pole than a mixer or recorder. Heck, worse case scenario you can always go to Home Depot and do the painters pole option until your Loon Audio or VDB pole shows up (broken in half and/or a million pieces.) I obviously have a lot of faith in our airline industry. :) Hey, they "lost" a bass guitar of mine for 2 weeks and it traveled more than I did for that gig!