I'm not sure what you get with a new boat (new boat, hmmmmm). But there are a few OEM items I wouldn't do without. The zodiac inflation guage. It's compact and relatively indestructible. Managing your tube pressure is important. I also have a zodiac bow bag. You could go with something from another manufacturer, but the bow bag is really handy and gets used a lot.
I really like the adjustable bench system, but eventually went with a fixed mount (no more play in the mounts when underway and no more wear at the friction points). That issue depends on your use or abuse.
I don't have the zodiac tie down sliders for my aluminum floor. I made my own with a ss steel d ring so I can easily lash down everything with straps that wouldn't easily work with the OEM track tie downs (there is only a small open eye on the zodiac slider stop). Either way, the track system on the aluminum floor is so cool and efficient you will want to take advantage of it. When you are flying you want everything secured.
Dry bags are awesome.
I now have a custom aluminum tank under my console bench along with my battery. Before that I carried a ten gallon tank strapped to the aft piece of forward wood flooring. My battery got strapped with a cam strap under the console or beneath the bench if I had bags going under the console. Getting the gas tank and battery forward was the best thing I did to improve the handling and bow rise of the boat. Note the battery is strapped to the track sliders and not the bench (more secure).
Smart tabs. They work. You don't need to do everything right off. The boat is going to be fun. But I can tell if I leave my tabs tied up instantly when I hit the gas at all. Less bow rise and lower planing speeds are a good thing.
The paddles on my zodiac were narrow bladed and didn't work well. Pathetic. I bought rafting paddles from NRS. They don't fit the aft paddle pocket on the boat. I added a small d-ring patch and velcro loop the paddle in place. Paddles. I use mine. What was zodiac thinking with those blades?
Running lights. Those after market suction cup battery operated lights are only good for slow speeds in the evening and dark hours. I also prefer to be seen. So it's 3 nautical mile rated lights for me (wired to my AGM battery).
If you run accesories off your battery it is a good idea to have a low voltage shut off wired into the circuit. That keeps you from running fishfinders, running lights or spotlights too long without the outboard on. If you pound around in your boat get an AGM battery that will take the shocks. Get a deep cycle battery no matter what. Reliability is prime.
Get a really good anchor. Those little mushrooms I see a lot of aren't all that helpful. I carry a small plow, eight feet of chain and 200' of line in a 5 gallon bucket with holes cut in the bottom. May not be necessary where you boat, but my anchor gets used a lot and I like the security to avoid being blown offshore in an emergency (hence the 200' of line). I know it's just an inflatable, but it is good to anchor securely wherever you may be.
Do I have any regrets? Well, I kind of like the used hypalon military models I see available locally, but they generally have the aluminum roll up floor (no track system) and they are black (delightful in Mexico, not). Just remember to store your PVC boat out of the sun and try to avoid a lot of heat in storage. It isn't UV that makes seams fail. It's baking your boat that does it. Use 303 UV protectant on your tubes, it works. Never use Armor All or anything like it, they make it almost impossible to get a good bond on accessories and repairs.
Sorry for the long post. I type fast? Just a few personal likes and dislikes about my zodiac. Your specific use will dictate your needs. Have fun!