Something to stuff things into to use as a pillow[pillows are a Godsend

]
A thermarest is better that a mat,where 'things' stick up out the ground, stones etc,a box airbed is best but is cold without a mat underneath it
Condoms.
If yer lucky enough to need them

.If not,fill them with water and chuck them at your competitors.
Tea light candles.
You know the little round ones in the foil cups.
In the make over shops,pound shops etc they are cheap as hell,as cheap as a £5 for a 100.Broken up they 'help' a fire grow and if its quite windless,then spread a few on the ground around your camping area,it really adds to atmosphere and helps define your area
Very handy inside the tent,its the cheapest form of light as replacement gas will be festival prices.
An Axe-Leaving this lying around deters criminal visitors
Water
Most important-Never touch the tap with bare hands

A 10 gallon folding container will limit the number of times you have to visit that bacteria infested hellhole.
Mixers-Bring enough for 3 ltrs of spirit,theres nothing worse than swigging the Rum neat out the bottle cos youve run out of things to kill the taste of raw alcohol
A folding chair to sit on[i cannot stress enough,the importance of a chair with a back on it]
A real espresso coffee pot-nothing finer than real coffee out camping,and it annoys those around you
You may come home with more than you set out with,and lets face reality thats most likely

So you'll need to bring some bags to put/carry things in.
Its the little things in camping that are so important to comfort

Pic below is mate Dave sitting on those all important folding chairs,spirits are on the table and we forgot to bring enough as mixers so had it neat that very same evening :x
Dog-Henry in the foreground/Charlie hiding behind the tree