Thanks Brad---that is very helpful,to know about dehydration and the fingerprints. I am fortunate in that I can sleep on the plane, and I may have gotten a little behind in my water consumption. I will try harder next time!
As for declaring things, I always err on the side of declaring everything, which drives my husband crazy. Coming back from a Canada ski trip I mentioned an orange! which I never imagined would be a problem as we had bought it in the US, took it into Canada ( and declared it then) and then brought it back unused. This not only got us sent to "secondary" but led to a diligent search of our car for more "contraband". We had to fill out a declaration form while they were searching and the agent kept asking, "Are you sure that it all?" before he let us sign the form. It took over an hour and was fairly humiliating, especially since I am a long-time federal employee with a security clearance to work in the federal courts. And my husband is still mad at me, but I do insist on declaring everything.
So the question on the customs form ( I still have it) is whether you are carrying " fruits, vegetables, plants, seeds, food, insects". I always answer "yes" because I am always carrying a bit of emergency food---I have the metabolism of a hummingbird and cannot go long without food. Peanuts ( roasted and packaged) are my food of choice, and I know they are OK to bring in, but the way the question is worded one must declare all "food." In fact the question is meant to identify plant and animal products that could be carrying pathogens or could propagate an invasive species, so it is too broad. The inspector was amused that I declared my peanuts. Apparently they do not care about these, as the beagle did not "alert" to my bag.
I understand the need to identify the products that could potentially carry diseases or bad organisms, and I have enough awareness to know what they might be---I do not bring in meat, cheese, tulip or other bulbs, fresh fruit, or anything else that could be a problem. But that "food" question always gets me.
When we return from South America I will ditch any food I am carrying before we leave the plane!