With military convoy I mean something alongside of: 10-20 armored trucks (medium/large) "shielding" the goods. Tanks would be cool but that would probably narrow down my choices a lot. Combat helicopters, at least 4. A unit of soldiers of 50-100 people.
A convoy like that is going to be stupidly expensive. Nuclear waste and POTUS are likely the only two things in existence that would prompt a government to spend that much money on it. At least, it's the two I can think of (and that's already an answer).
Of course, a private company/person may use as large a convoy as they can afford... provided they find people willing to organise such a transfer. Any serious private security company would probably just recommend the bare minimum of trucks to fit all of the cargo, with a couple armed guards for each. If you were to ask them for a superconvoy, they'd probably not want the hassle or the risk associated with it without a bloody good reason.
Let's look at the requirements.
10-20 armored trucks (medium/large) "shielding" the goods.
That's a lot of trucks. You may find that many vehicles in a few convoys, but certainly not all would be armoured trucks. For nuclear waste, the armour is strictly a function of containing radioactive material safely, and the truck is just a bog-standard truck. The rest of the escort would ride in military trucks or jeeps, which wouldn't need to be armoured. For POTUS, the only armoured vehicle in the convoy is the limo. The rest is once again just bog-standard vehicles, because the people inside just aren't that valuable.
To warrant a dozen trucks or two, you would need to transport a lot of equipment. It may be particularly big, or particularly heavy, or each piece may require to be isolated from others, but it's an unusually large quantity regardless.
No passenger transport would warrant that level of protection, and if it did you just wouldn't do it that way.
Tanks would be cool but that would probably narrow down my choices a lot.
Combat helicopters, at least 4.
Tanks are slow, tanks are not gentle on the pavement, and tanks are generally impractical for anything other than the combat they were designed for. You could replace them with some kind of Humvee with an anti-tank turret to keep a comparable firepower, but why?
Combat helicopters are also a bit overkill. You could have a couple in case of extreme emergency, but they would most likely be an stand-by at a nearby airfield rather than in the air constantly.
The big factor here is your threat model. What are you realistically expecting to fight that you need a tank and combat choppers on your own soil for? I can't really imagine a scenario where those would be useful, and so I can't see a reason to bring that kind of weaponry or armour in the equation.
What you would most likely have is an observation chopper flying above the convoy, another on stand-by to take over. A particularly large convoy may warrant doubling that number, with either choppers over front and back half of the convoy, or one above the convoy and one scouting ahead.
You could also imagine a couple helicopters with assault teams on stand-by, but there would be very little to be gained by having them in the air constantly that wouldn't be accomplished by having them in a jeep even just X minutes behind the convoy.
A unit of soldiers of 50-100 people.
That much manpower probably comes with a convoy of that size naturally. If you have two dozen vehicles, put four people in each and that's already the required amount of guns. A convoy that big would require the cooperation of local police, and so some of the armed personnel in the convoy would have to be law enforcement rather than military or private security.
What are you transporting?
You can forget about art, collector's items and such. These are simply not worth the spending.
Looking at real world examples, we have nuclear waste and POTUS. So basically anything that can potentially level the country. Nuclear warheads, top secret alien debris, experimental superweapons, a real-life Superman, etc. Whatever it is, it has to blow your mind. I have to insist on that. Being high value just isn't enough to be worth the hassle, it needs to be a game changer if it falls in the wrong (i.e. not your) hands.
And again, either you have a lot of pieces, or the pieces can't be safely stored together, hence why you have so many trucks.
You also have to consider one last thing: it would be less conspicuous to move one truck at a time than have one giant convoy. The main reason you'd go for a superconvoy is because time is of the essence. There is some emergency that requires all of the goods to be transported ASAP. Otherwise, you risk much less by transporting them one at a time. Especially if you need all the parts to assemble your doomsday device, or whatever it is you transport.