You could be forgiven for assuming that The Royal Family can eat whatever they feel like when travelling abroad, but apparently, this just isn’t the case. For starters (and main I assume) they are forbidden from eating shellfish because of the risk of food poisoning. They are also advised to avoid meat cooked rare and tap water, among other foods and drink when overseas. The precautions are in place to prevent them getting sick and being unable to perform their duties on their busy schedules. Reportedly the Queen plays by the rules, but some of the younger royals are known to play up and eat whatever they feel like!
By Carfax2 (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons