Anyway, here's what I do: I measure a dose into one of those little sample-size liquor bottles. Yes, I suppose it DOES look a little odd to be pouring a child a shot (though I feel like most parents would nod understandingly and wonder only why I wasn't pouring another for myself), but I generally administer it in the privacy of the bathroom, or in the car, or from behind a large fast-food soda cup. Plus, I bring a dosage cup so that the child is not actually seen drinking DIRECTLY FROM a liquor bottle.
First I measure out a dose of the medicine I want to bring with me. Then I pour it into a little liquor bottle.
Usually I peel the label off the bottle to make it look less seedy, but this particular label was leaving a ton of sticky residue and I didn't have time to mess with that so I just left the label on. I have a tiny little funnel that makes it easier to get the medicine into the bottle, but I've also just carefully poured it.
Then I rinse out the little dosage cup, put the cap on the little liquor bottle, and label a baggie with what's in there. I also put down when to give it: I've been surprised at how easily I can forget what time I gave the last dose. Sometimes I'll add a note about exactly how much medicine it is ("two teaspoons" or whatever), if I plan to have the medicine along for an extended amount of time---if, for example, I were making an emergency single-serving of Benadryl to keep with me.
The baggie is for easy labeling and also for in case of leaks, but it's also because AFTER the dose of medicine is given, the dosage cup will be sticky and I might not have an opportunity to rinse it.
I put the bottle and the dosage cup into the baggie, and the baggie into the diaper bag.
I HAVE worried about various open-container laws. But it seems like the odds of me being pulled over on a particular trip, AND of the officer deciding to search the diaper bag, AND of the officer not believing me (or believing his/her eyes or nose) that it's cough medicine or Benadryl in the bottle, AND of the officer thinking that what he/she has mistaken for 2 teaspoonfuls of liquor (1/3rd of an ounce) is worth making a fuss over---even if ALL those things went wrong, a test of the substance would vindicate me. I imagine myself in court saying to the judge, "You see, your honor? I was telling the truth ALL ALONG." Music swells, courtroom cheers, officer looks mortified and starts stammering, judge apologizes fervently that the state has so flagrantly wasted the time of an innocent citizen, etc.