13 year old not eating or drinking

I recently took my 13 year old godson to Italy on vacation for 10 days. He did not like the food and actually said that he did not like the taste of the water. So all he drank or ate all day was 1 coke. He’s a skinny kid and we were walking around Rome, so of course he got tired and cranky. I don’t want to force him to eat and drink, but we couldn’t seem to find any food that he liked, (except for gelato!) I understand how to handle this if the other person is an adult, but this is a child that I am responsible for… in a situation such as this, how can I help him, please?