You may find her appetite decreases when you are away becasue of the heat, so she might be quite happy with snacks like little sandwiches or pasta salad or cold toast with cream cheese and fruit - she will need to keep her salt up so I wouldn't worry too much about giving her a few baby type crisps as well. if you are out at a restaurant or cafe, you may find something on the menu suitable for her to snack on, even if it is only bread and butter and just make sure she gets a good breakfast and plenty of drinks and if you are self catering, a good familiar meal when you are there.