Best twenty quid I spent all year was a bag of travel meds. also helped 3 unprepared friends from migraine etc. Conceivably, the loperamide could save a life if you're with poorly infants.

Added the marvellous cough suppressant ACC and antacids to this:

https://www.lesswrong.com/posts/LJw98jjiZDBKiZxKB/jetlag-nausea-and-diarrhea-are-largely-optional