I heard TSA and other security groups get most nervous about unmarked packages. I would put the packets in the box they came in my checked suitcase. That gives them more credibility. I wouldn't pack any silver packets that did not have pre-printed labels on them, like "tomato basil soup".
On my first trip to India, I did not have time to get all my shots, so I brought 5 days worth of power bars in my suitcase and just ate them the entire trip. Not very entertaining, but I didn't pick up any stomach bugs either.
I was on one flight where they filled the plane with insecticide before they opened the doors for us to deplane. Apparently they didn't want any flies (or malaria-laden mosquitos) to deplane with us. I can't remember which two countries I was between on that flight. I'm sure they don't do that between US and Ireland!
The biggest problem with food stuffs is fresh food that bugs can hitchhike on or that plant seeds or spores can ride over with. Generally, packaged and processed food goes across borders without incident.