Congrats and welcome to the forums.
The basic list for me at least:
1. Drinking hose, the white ones made just for RV's.
2. Sewer hose.
3. Two sets of chocks for your tires. I also have the x chocks. I use them both myself.
4. Either some 2x6's cut down to drive up on to help level it, or a set of "better blocks". They are kind of like giant lego's you can use to drive on to help level your trailer. Again, I carry both. LOL. Guess it is the boyscout in me, I like to have plenty of everything.
5. I personally really believe in using an extension cord instead of dragging the cord out of my trailer. They are kind of pricy, but IMHO they are easier to wind up than stuff the cord back in.
That is just the short, short, short list. I am sure others will chime in.
99% of the above can be gotten at most Walmarts, or at any camping world store. You will pay more at camping world, but if you go to one, you will spend a ton of money there buying other stuff. LOL
If you do go to camping world, I think the good sams membership is worth it then. With the discount you get with the membership, doesn't take much at all to pay for it in savings.
Almost forgot, ask your dealer what you get with it. Some will give you a "starter" pack of stuff or a discount at their parts store. Check into that before you buy anything.
When we bought ours, we got a 100 bucks to use in their parts store.
2015 32 Foot Rockwood 8289WS 5th Wheel
2013 Chevy 3/4 Ton TV