Essential item number one, see the picture below, of course, you need the camera and the tripod, they are without doubt the most essential. The other essential is the chair, foldable and light, you can hang it on your belt. It will make your wait for the waders comfortable, it will also keep your back-side dry if you decide to take some low level shots of waders at the mud-flat.
The second half of the year brings much more rain to Tawau than the first half, and I have more free time during the second half. The rain has washed out a few of our planned bird photography outings already. So, the other essential is to let your camera wear some rain-coat. Here my camera is fitted with the Think-Tank Hydrophobia.
With it in place, I could walk with my gear with peace of mind even in the most severe overcast sky. Since the Think-Tank cost more than the poncho that I wear, my bird photography friends have concluded that I love my camera more than myself, in other word, a total idiot or TLG in short.
If the rain gets havier, you can always let your flash unit use the umbrella, as seen here.
I got this camouflage netting via eBay auction, 5 feet tall by 9 feet long, it can be handy for hiding yourself from view. You can sit behind it to enjoy your snack while observing activities through the netting. Here is the picture showing my camera from behind the netting.