We love our 2010 Odyssey! Ours came with the roof rails ... they make the van look nice, but can't speak to how they perform, as we haven't had to use them. We did purchase the door edge guards (especially for the front doors); they help a lot in parking lots and the garage (so I don't scratch my husband's car doors). Highly recommend them. As for the ones you specifically asked about ...
We have the Cargo Mat and Cargo Tray. We ordered the mat, but the dealership messed up and ordered the tray instead. The service guy was great and told us to keep the tray and then gave us the mat too! Both are great ... the mat helps to protect the carpet and the third row of seats from things like the dirty wheels of the stroller. Since we primarily use the second row of seats, the mat gets the most use, but the folding seats still fit in the cargo area with the tray in. When we put up the 1/3 seat of the third row, we just fold the mat over. If we need all the seats up for some reason, we just take the mat and put it in the tray. Tray is great ... the Graco stroller will stand up in the tray with no problem and still leaves plenty of room for my "collection" of reusable shopping bag to sit next to it. All in all, I really like them both and am happy we have them. As for the cargo net ... we bought a less expensive one on-line (I think), but we never use it. And the cargo organizer looks neat, but I think it could be limiting in how you may need to rearrange things from time to time.
I also HIGHLY recommend the hitch ... we don't tow much, but with the hitch, you can have a bike rack or one of those extender trays. Not sure how we would have gotten to the beach with my niece's bike and all the stuff we needed for our (then) 7 month old without the hitch. I know it seems crazy to have Honda install it for you, but because they have to do some changes to the transmission for hauling, it really is worth the extra money in the long run to make sure your van is safe for towing.