One of the challenges of exploring a foreign city or other area of interest is keeping yourself fed and your energy levels up. Although most places have plenty of snack bars and restaurants, the food can be overpriced and you may have to queue. In some parts of the world you may also be justified in feeling a little uneasy about the standards of hygiene in which the food has been prepared.
On the other hand, lugging your own food around cn be a tremendous pain, especially if you are also dealing with a family of young children. Unfortunately it's the kids that benefit most from eating little and often - they're also the ones who will let you know most vocally if they're feeling hungry!
A great solution is to carry a small rucsac or fanny pack (a 'bumbag' if you're a Brit) containing light snacks to keep you going through the day. The sort of food you carry should be very much governed by the type of place your visiting. Clearly, it's not a good idea to walk around an African city in the heat of the day carry rapidly melting chocolate or other foods that might spoil easily. Whatever the climate, you also need to take care not to pack foods that are highly frangible or that squash easily; cake and sandwiches generally aren't a great idea unless you seal them in plastic boxes, which can be more than a little unwieldy.
Nuts are good, providing nobody in your family is allergic to them. Although doctors advise against ready-salted nuts, they can be very useful in hot climates where you're sweating a lot and need to maintain a salt intake. Don't forget to drink lots in such a situation! Another good staple is dried fruits such as raisins and sultanas. Larger dried fruits, such as dried apricots, are very tasty indeed but tend to be a little less popular with kids. Fresh satsumas, tangerines and clementines, despite their softness, are surprisingly durable, and will survive much better in your fanny pack than an apple or a banana, either of which will rapidly become bruised.
Chocolate and candy can be useful if you're out in cold weather - consumed in small amounts, they are a good energy fix and they shouldn't melt if the temperature is sufficiently low. Try to combine chocolatey treats with more savory foods so that your kids are getting a healthy balance and not too much sugar.
It's a really good idea to do a little research before you travel about sources of cheap, quick food in your intended destination. A little forward planning can save you having to carry to much around with you, or having to spend valuable vacation time hunting around for a cafe!