basic cleaning gear including a lens cloth, a cloth for wiping down the outside of the camera and a bulb blower
UV filters (for protection
polarizing filters for most of my lenses. These are great for cutting out flare and have a considerable impact when photographing water, glass or sky
external flash units can be very handy to have while you travel although can add significantly to the weight of your kit (and you’ll need more batteries for them of course). The improvement in results from using a dedicated flash that can swivel, bounce and with manual controls are significant over a built in flash
The main thing is to pick something that fits everything in and that is comfortable. You should also consider how weather proof the bag is as well as how much it looks like a camera bag (and therefor makes it a target for theft)
clipped from: digital-photography-school.com