A mat for outside the tent where people an take shoes off. As much extra warm stuff for bedding as you can fit in. A complete set of warm clothes for the evening that can go over your day clothes. If it's cold you will want to put jammies on over your day clothes.
Night time toilet considerations, if it is wet you will need wellies to get to the toilet, if the toilet is a long way away accept you will need a designated pee area (or take a portable toilet)
If it is going to be wet or even damp at least 2 changes of clothes a day for smalls.
A shelter to cook under, if you are cooking fatty food and it starts to rain it will explode!
Don't take too much food it will just go to waste.
Clothes pegs, glow sticks, string, head torches, gaffer tape, batteries, cables for charging, beach shelter if you plan on a day at the beach, water bottle, solar lights, frisbee, football, boule, towels, cooking oil - these are all things I usually take and have forgotten at least once. (Tie glow sticks to children at night time)