Don't worry about weight IMO. In the end, plus or minus a few pounds on a cat or raft doesn't mean squat. I like dry boxes even for day trips. I also like a cooler rack even on a day trip. If you haven't gotten a rower's seat yet, be sure to get the short back one.

The NRS fishing setup is pretty sweet with the platform, hip bar and swivel seat. Very comfortable. I don't know how it fits on a cat, though.

I wish I had some pictures of my setups, but I don't have at this point. I also wish I could help you more, and I can't think of a single piece that you MUST have. At this point if you can dream it and have some technical know-how you can make the rig that best suits you. If you've spent any time on the river you will have noticed by now that everyone has a different setup. Of course the dollar decides all of this in the end.