Duzzy, it occurs to me that you should just take your best guess at the gear you'll need, based on your own personal preferences, then go out and do a three day hike with your set up. See if it works for you. Then, when it comes time to do an actual mission, at least you'll know that what you have works for you and you can make adjustments from there.
I know, you'll probably end up having to back track some after you find out what the reality of a SAR mission is, but at least you'll start out with a setup that you are personally comfortable with.
Something mentioned in this thread, but which I don't think was stressed enough, was for you to find a good way to carry things in front of your body. Even as a recreational backpacker/hiker, I'm forever looking for better ways to carry gear in front of me that doesn't add too overly much to my heat loading.
Last weekend on an overnight hike in the Sierras, I put the following on my front pack:
- GPS
- Compass
- Video Camera
- Camera
- ACR PLB
- Cliff bar
- Mini gorilla pod tripod
- StickPic
- small flashlight
- spare batteries/SD cards for the cameras
On my hip belt (which is set up for this kind of thing), I was also carrying:
- Water filter
- lunch
- PSK (easily removed for when I take the pack off ... contains a SAK, a few bandages, spare compass, fire making gear, signaling gear, etc.)
- Busse SAR-3
- sunscreen
- bug repellent
- work gloves
- fishing gear
- fuel for my camp stove
(Maps and bandanas were in my pants pockets.)
Without any trouble at all, I can add a hand held HAM radio to the mix. I haven't yet, mostly because I doubt it's utility in the back country, but I can easily do it if I find a justification for it.
Except for the camp stove fuel (which was just there to balance the belt more than anything else), all that stuff is there because it's stuff that I think I might need as I'm wandering through my day. Not only does it help to balance the load on my back, but it's also terribly convenient. I LOVE being able to get at gear without taking off my pack. And some stuff (like the fishing gear), is nice to be able to get easily get at, even though realistically I'll be dropping my backpack to use it. By organizing my gear in this way, I don't have to get into anything on my backpack until I reach camp -- well, except for my hydration bladder if I decide to refill it at some point during the day. But that hangs on top of all my other gear on the backpack, so it's just as easy to get at as anything on my front pack.
I have to imagine that a SAR team member has similar needs, only possibly much more urgent.
If I was you, I'd give a lot of thought to front pack setups. There have been some suggestions offered up-thread. Pay attention to them. They look like good suggestions to me.
(By the way, the front pack that I use is integrated into my backpack by the manufacturer, so unless you're going to start using a Molly Mac Pack, what I use is not an option for you. Just thought I'd forestall the next most obvious question.

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