Probably the best thing you can do if you're a first time RV owner....whether buying new or used, sit down inside and think of the things you need for YOUR situation. Paper towel holder, towel racks, shelf organizers etc. Same with the outside. Do you want leveling blocks or do you have a 2x10 you can cut into blocks.
X10 on the starter kits. The sewer hose in the first starter kit I got leaked the first time I used it. And the fresh water hose had a cheap plastic connector that stripped out as soon as I tried to tighten it. You're not missing much if you didn't get a starter kit. Everything in there you will replace before your first season of camping is done. We've bought 1 used and now 2 new, all from a dealer. Each time it was a pleasant gesture to receive the "starter kit" but I have quite a collection of cheap pressure regulators and 30-15 amp adapters.......about the only thing in there I've hung on to.
The only other thing I would suggest is DON'T get all hung up on buying RV specific items without shopping around. Things like refrigerator or cabinet bars that are $10.00 a pop at the RV store are nothing more than spring curtain rods you can pick up at any Walmart for about a buck each.