It really all depends upon the trailer manufacturer and the dealer what's included with the original camper. If there is something you specifically want, ask up-front BEFORE signing the dotted line.
For example, if the camper you are looking at has a manual tongue jack, you might ask they include an electric tongue jack in the mix. If they can't include it in the selling price as is, then you need to request it be installed before you take delivery and simply pay the difference out of pocket for the service and part to install it.
Our last camper did not come with an electric tongue jack. We wanted one after 2 previous campers with manual jacks. We also wanted Max Air style vent covers over the vents. So we had them install the items before we took delivery. We signed the papers, and then they added the new parts. We paid a separate bill for the parts, everyone was happy. We also got a 10% discount on the day of purchase, so that was a big help also. BUT, they did give us a socket wrench thing with a long shaft, which is a tool used on the end of a drill to manually attach to the electric motors to move the slides in the event of electric failure. That was not included, but I asked specifically for the right tool and they went ahead and gave it to me. (no charge).
The items that came with the camper was the jack handle for the stabilizer jacks and installed jacks, 2 propane tanks, battery, spigot for outside kitchen sink, a 10 foot sewer hose with connections, a package containing the wall mounted toilet paper holder, bathroom towel holder, soap dish holder (I never installed any of these), the clips to hold the refrigerator door open to keep it from smelling when all power is off, and a boat load of manuals.
Pretty much, you don't many extras. You may, or may not get the starter pack (10 foot sewer hose with ends and clamps, in-line garden hose pressure regulator, maybe some extra lug nut covers for the wheels, and depending upon your camper, the bathroom soap dish and toilet paper holder that needs to be mounted by you.) You may also get a complementary sample of black tank chemicals (it it really will be only a "sample").
Basically, what you see is what you get though. To out-fit the camper, (bedding, dinner ware, cook ware, camping gear) is all on you as every one of us does it different, your specific needs will be just as different. When it comes to camping and RVing, no 2 of us are alike ... ever.