It's usually possible to persuade a dealer to reduce the selling price of a caravan and / or include some accessories as part of the deal, especially when there is no part exchange to trade with but it looks as though the deal has already been struck by Lisa, so it might be a bit late to haggle now. No harm in trying though
Must Haves:
There should be an ehu ( electric hook up) cable with the caravan when you collect it Lisa, as well as a step (of sorts) and a waste water container. Ask about these during the handover.
You will definitely need a leisure battery, if you are planning to fit a motor mover (helpful if you have trouble reversing the caravan) then choose a 110 amp/ hour battery which will cost between £80 - £120 depending on which one you buy.
If you can persuade the dealer to give you a battery ( unlikely) so much the better.
Some caravanners use melamine lightweight crockery, some like us prefer normal crockery but we don't carry a 6 setting dinner servive, just a couple of everything plus knives and forks from Wilkinsons or Argos.
You are always in with a chance of persuading the dealer to part with an awning, if you don't ask you won't get.
If you use an awning you will need at least a breathable ground sheet, I should imagine that you will be familiar with these from your tenting days. A camping table and lightweight chairs would be handy for your awning too.
A wind up LED torch comes in useful for walking back from the pub in the dark, and a led lantern is good if you enjoy sitting outdoors when the light has faded, although the caravan will have an awning light anyway.
We use plastic boxes from the pound shop if we take tins, bottles etc with us, we put them on the floor over the axle in transit which minimises the risk of heavier items falling out of your overhead lockers and ruining your worktops as you begin to set up after a journey.
As Sir Roger mentioned, always look for your caravan stuff in supermarkets (especially crockery towels and bedding), Wilinsons, Argos (flat screen tv with freeview) before buying from dealers accessory shops because anything with the word 'caravan' written on it attracts a huge mark up for the retailer. Aldi and Lidl often sell caravan related goods at affordable prices too.
Save a list of things that you need to pack on your computer and print a copy whenever you go away. It won't prevent you from forgetting things but you can have fun compiling it and blaming your other half for forgetting to remind you to check the list.