It's surprising at how little this matters.

I came back from a tech event once with a build a robot kit, except I'm a very light packer and the box was huge so I had to take everything out and fit it into a backpack along with everything else I had.

I had a compartment that had an assortment of circuit boards, screws, wires, plastic pieces, etc..

No one even batted an eye and the bag went straight through the carry on x-ray machine. This was in San Jose, California while preparing for a cross country flight. I was surprised too.

They aren't looking for electronics - they are looking for large masses that could be fuel for the explosives. Big blocks of clay, liquids, etc. A jumble of electronics alone with nothing that can actually explode is common and doesn't ring any alarm bells. I discovered this after talking to a TSA agent after flying a few times with my modular synthesizer, where I was surprised that it was never pulled for extra screening.

My mother makes soap and tends to give me a few bars when I visit. I have learned to mail it back to myself; taking a few 2"x3"x5"-ish blocks of a uniform-density material through the airport is a guaranteed close look.

What I'm reading is that it's possible to sneak a bomb through as long as the bomb smells like lavender.

Magic the gathering decks (60-100 cards) also seem to trigger this as they also show up as dark blocks on x-ray

Yes, baby wipes will get you searched every time. They just look like dense bricks of material on the x-ray.

Same for a rectangular pack of biscuits.

They closely examined the cucumber in my bag

Drugs hidden in a cucumber truck:

https://www.chicagotribune.com/nation-world/ct-fentanyl-bust...

Also, plants or foods are sometimes forbidden because of potential to carry vermin, plant diseases, etc.

https://www.cbp.gov/travel/us-citizens/know-before-you-go/pr...

A friend once forgot a bare PCB TV-b-gone in a coat pocket while traveling EU to US. He noticed it right at the first checkpoint.

They asked what it is, laughed at the response, and went "eh, as long as there are no wires dangling off it, we don't care." He stuffed it in a bag and had no further issues.

Why the wires would've made a difference is beyond me...

You obviously don’t watch Tv shows like 24. Wires is something you stick into the explosive.

A year or so back my son and his friends built a muon detector as a high school project, and then flew it from London to Germany and back to measure muon rates at altitude. Basically two metal boxes glued together, with some hand cut holes for display and power. Inside, a large block of solid plastic scintillator, wrapped in foil, with a bunch of hand-made electronics connected to it. Suspicious? Only a bit. I wrote a letter on headed university paper, explaining what it was, and with contact details in case they needed to phone.

At Stansted, the kid carrying it got the third degree, eveything put though the explosives sniffer, and so forth. The security person afterwards told him it ticked all the boxes except one for a bomb. Would love to know what that one was! They did eventually allow it on the plane though, and got really good data from the flight.

On the return flight, security at Cologne didn't look twice - just went straight through the x-ray machine, didn't even get pulled aside. Must have been asleep on the job.

When in university, I took part in a CUBEsat effort.

I brought the mechanical assembly -no electronics, just the aluminium structure- of our satellite to CalPoly for a CUBEsat workshop; on the way back to Europe I found out the hard way that anything which goes into space is considered munitions as far as the US DoD is concerned.

Took a while longer than expected to get on my flight...

ITAR not just DOD.

The TSA did an internal audit where they sent 70 mock explosives and weapons through checkpoints. 67 made it through.