I am one of those that disagree with buying "Used" (edit) for your first RV. We had our first pop-up (brand new) for over 6 years and then moved into an 18 foot travel trailer (brand new). Our second and third travel trailers were brand new also. Sometimes, its NOT always about buying an RV for future resale, but for buying an RV to use it for what you need and want at the present time. Once "it" serves its usefulness, it's OK to sell it and move on to something different. There's still something to be said about being the original owner and knowing every second of history about the camper and experiencing the "new camper" smell. And here again, it's NOT always about the money! But then, maybe it is? Trying to get an RV loan on a used unit is much more restrictive than getting a loan an a brand new one! There is some truth to be said about first time buyers and trading within 2-3 years, needs and wants change, families grow and decrease, life situation changes things, and all of us could be dead in 2 years also! So my advice is.... if it makes YOU happy, that's really all that matters... new or used! Because, YOU are the one who has to live in it, and YOU need to be satisfied you've made the right decision.
Back to the OP's question now. When purchasing a new camper, it should come with a battery and the dealer should have the courtesy to fill the propane tanks. If new, the dealership will be doing a PDI (Pre Delivery Inspection) with you, or a "walk through" demonstrating how all the items in the camper work and to verify everything is working to your satisfaction before you take ownership of it.
The PDI cannot be accomplished without a battery and fuel in the propane tanks. So they will fill them.
After that, anything else the dealership throws in is extra gravy. Usually, they throw in a token "starter kit", which consists of a 10 foot sewer hose with connections you'll need to put on yourself, a garden hose pressure regulator, some samples of black and grey tank deodorizers, and a bag of extra parts. That bag may contain some extra lug nut covers for your wheels, the toilet paper holder which you'll need to install yourself, and maybe a few extra color matched cabinet screws or hinges (maybe).
In addition, if you have slides, they should also include a wrench for manually extracting the slides, or an adaptor that fits on an electric drill if yours does not have an actual override manual crank. They will also include an awning puller (if yours is a manual awning) and the crank handles for the 4 stabilizer jacks at each corner of your camper (unless you've had installed electric jacks.) If your camper does not have the stabilizer jacks as part of the original deal, I'd insist they be added.
Your camper may or may not come with an electric tongue jack. If it does not, you may be able to negotiate an electric tongue jack into the base price. None of ours came with an electric tongue jack, so on our 3rd camper, we paid the price for one and had them install it (labor free)... so we got a little something extra out of the deal.
You may be able to negotiate for a power surge protector or an EMS, but most likely, you'll have to buy that separate, but they may install it at no charge.
Your camper should come standard with a spare tire, but here lately, its a trend to not include spare tires. So, this is another item you may ask them to throw in if the camper does not have a spare. Make an issue of it, and you may get one.
When you purchase new, it's a good opportunity to negotiate items like Max-Air roof vent covers too. Here again, we purchased some knock-off brand vent covers for the roof, but the dealer installed free of charge.
Our last dealer gave us a 20% discount at their RV parts and equipment store for anything purchased on the day of the sale. That's why we ended up getting the vent covers (3 of them), the portable surge protector, and the electric tongue jack.
Until you sign the final paper work, you do have a lot of negotiating power. The dealer can always say "no" to a specific request and offer it at your expense, but why not try anyway? You've got nothing to loose and everything to gain.
If you can get them to throw in a garden hose, an extra roll of toilet paper, a fire starter, tank chemicals, anything, ... go for it! But if not, don't cry over it. Apart of the cranks for the stabilizer jacks and the toilet paper holder, they really do not have to offer anything else.
