you may need a booster pump, depending on what RO system you get and water pressure (I got mine from Gaps water, they have a DIY package that is easy to put together and all you need).
You may also need a length of preferrrably 1 inch hose to move water from IBC to van, depending on distance and height, you may also need a transfer pump (available from B and Q for about £35), I use my booster pump which transfers about 90 litres per minute 100 feet to the van.
We also got some bollards to put out if you are in public areas, to cover yourself in case of accidental trips by members of the public!
Also an electric fan heater or oil filled rad for the van/tank storage area. Guessing you have 12 volt charger for recharging leisure battery (just checking, you had earlier forgotten poles and reel)
Is handy having some spare connectors too, if you break one part it can scupper you for a couple of days, when i ordered poles etc from gardiner poles i also got a spare of everything that was likely to get damaged.....