Were I to start searching tractor trailers, immediately following an EMP, I’d be hitting the refrigerated units before the food spoils completely and getting everybody involved, friend or not.
If for no other reason, that food may get into needy hands instead of spoiling.
And the bad guys, if they got some may remember me as a square guy later. Might help, may not.

After that, the manifests.
An interesting thought, I can’t say that I’ve ever read of anyone thinking of that and it’s a different thought.
I daresay that most companies, if they survive will be filing insurance claims on everything. Especially the refer units.
The insurance companies will likely go under, so it’s a tough call on who to contact or if. Definitely if.

Theft? Or just using something that will rot/spoil and be ruined if left.
Morally/ethically, it can be argued from every angle.

More than a couple of days? I would avoid the refer units for the most part, again the spoilage.

First day(s), I’d be gathering my own stuff together.
Making sure what I have/need/want. Making sure the kids and wife truly understand the new rules:
Waste not.
Reduce, reuse, recycle, repeat.

I’m in an unusual situation.
My wife works in emergency services. (I used to, ex-LE)
She will be picked up to work, on horseback if needed.
I’ll likely be put to work by either the local PD or SO. They know what I used to do, and in that situation, it’s gonna be all hands on deck.

I’d probably hit all the neighbors to see how everybody’s faring, if anybody needs anything and such.
It’s a fairly close community, very friendly and helpful to all.
They know what I do, I know what they do.
Our kids go to school together, and almost everybody preps here.
(There are advantages to high LDS areas)

For most here, it would be more like a long term snowstorm where the power goes out.
Just a little more complicated.

Milk, fresh fruit and veggies would be the difficult issues around here.