Don't doubt the power of a plastic bag. A plastic bag is your friend - from the snack-sized Ziploc, perfect for a packet of string, earplugs, paper clips, band-aids, and tissues, to the all-purpose garbage bag - for litter, for sitting on, for wrapping your camera bag in during a storm, and for a rain poncho - they'll serve you well and cheaply.
For rain, I made up a thing I call a Rain Bag - basically it's a large sandwich bag that has a circle cut in the center on one side and a small rectangle cut near the top edge of the other side. When it rains (or snows, or on a windy beach), I simply pull it over my camera, pushing the lens through the hole and the viewfinder through the small rectangle. It'll take three or so tries till you get the measurements just right, and when you do, just lay the bag flat, put a piece of cardboard in it, and trace out where the holes are - now you have a form that you can simply slip into any new bag and use an exacto knife to cut out the holes.
As for the polarizer and lens shade, that, too, can be a bugger. I actually left my lens shades at home for years 'cause of it. But this year I finally saw just how much of a difference it makes to have a lens shade on.
I was going to cut a small hole in the side of each shade (especially the telephoto zoom), figuring that a small hole is better than no shade at all (I also thought of putting black cloth over the hole, to flip back in place), but I've actually found that I can use my left index or middle finger if I reach across the lens and push up on the right edge of the polarizer.
Remember to always push up - if you turn it to the left too many times, you could well unscrew it, and then you'll have a very expensive piece of glass bouncing off a pier.