It does depend upon where you are going and what the facilities are like (if you have any, that is).
Single inflatable air mattresses and the foot pump to go with them.
Some very warm socks, woolly hats, gloves, a hoodie and jogging bottoms, quick dry vest and soft shorts for sleeping in. An oversized waterproof that zips up the front. Wrap the sleeping clothes up in a plastic bag every morning so that, even if it rains and the tent leaks during the day, you have dry, warm things for night time.
A three season sleeping bag and a cheap fleece blanket each.
Gaffer tape and thick bin bags - ideal for emergency tent repairs.
A powerful LED torch that you can clip to your belt loops/is always to hand.
Tick removing tool. (And if you get bitten, make a GP appointment for the day after you get home - many treat preemptively now for tick borne diseases). Longsleeved tops and socks big enough to tuck your trousers into them keep the little bitey bastards out, as well. Always take outside clothes off before getting into bed and put them in a separate bag outside the main part of the tent in case any of the fuckers have hitched a lift.
Bug bite cream (Waspeze?) and mozzie repellent.
Sunblock. Sunglasses. Sunhat. Paracetamol. Antihistamines.
Toothbrush, toothpaste, brush, hairbands, small bottle of unperfumed soap/shower gel for washing hands, hair, body, etc, a couple of flannels.
Sanitary protection. Even if you're not due on, as you don't want to be in the middle of a field and find out that you've come on early.
A fully charged powerbank for your phone, spare charging lead and plug/adapter if you have access to electricity.
Once you've got those things packed, it depends upon whether you are driving there - if you are, you can faff about with all the other nonessential stuff.
Practice putting the tent up and taking it back down again. The pop up ones are easy when you know how to do them, but potential comedy gold when you don't. If you need tent pegs, buy a packet of spare ones, a large bottle of water for moistening the ground to help get them in if it's been dry and a mallet for knocking them in (stamping on them bends more than you'd like). Take your time putting it up - rushing leads to mistakes like snapping poles glares at DP for doing that on the test run and you can make sure that there isn't an essential bit missing, such as a top piece that keeps the water out glares in the direction of Black's for not putting that bit in the bag last summer. Take time to make sure that what you're pitching on isn't sloped (you won't want to be sliding down the tent at night), doesn't have an ants' nest, sharp stones or is too close to water/the toilets/shower block/the exit to ever get any sleep.
We do it regularly - as long as you are warm, dry, uneaten by insects and aren't feeling every single little lump and bump underneath you, it's fine. But you might be shocked at how cold 4.30am is even on the hottest days, even when it doesn't rain.