Vested Interest has vests designed to carry just about anything and will custom design a vest to your specifications. You must however, consider your needs carefully, as it is counterproductive to have too large a vest. Ideally, you want to carry everything that you are likely to need on a given photographic outing. Other items that are helpful are a lens cleaner, flash, lenses, teleconvertors, extension tubes, filters, and sunscreen. For extended outings consider carrying some food and water.
Numerous pockets are advantageous.
The downside to many storage sites is that unless you develop some kind of system for finding certain articles, they will invariably become lost. When evaluating a vest, it is wise to bring your camera and accessories with you. This is important because you want to be sure that your camera and accessories will fit into the pockets. Placing some items into a back pocket will balance the vest better and prevent the collar from cutting into your spinal column. In summary, the ideal photo vest will allow you to carry all the gear you really need, in a manner that is logical and accessible.