Here is the basic stuff we bought when we got our camper. Most of it we bought new but some got things redeployed from the house/garage to the camper.
security: set of 6 keyed-alike padlocks, hitch-lock with chunky pad lock, bike chain
lighting a fire: fire starters, matches, axe (or tommahawk), gloves, folding shovel
eating: set of plastics plates, cups, plastic wine glasses etc
cooking: set of cutlery, utensils and pans that can live in the camper
site setup: wheel chocks, camec level, bubble level, portable clothesline, c-gear mat, picnic rug, rubbish bin, tarps, rope, camp chairs, folding table etc
comforts: bug spray, first aid, sunscren, candles, washing up stuff, rags and towells
others: 3-bar lighting kit, arb fridge, torches, gas fuse, toolbag, recover hitch for camper, small step ladder, small toolkit
Stuff that we bought early on but probably didn't need to:
an extra folding kitchen
a folding/collapsible wardrobe
ring burner bbq
large folding table (we downgraded to small table, much better)
Stuff that we bought later, that we wish we got earlier:
solar and extra batteries
chemical toliet and shower room
inner spring mattress
water pump