A solid water bottle (metal insulated ones that can also hold hot water are my go-to, as it means I can carry a lot of tea around on my person without having an IC mug)
Hiking boots you have broken in before field
Flip flops/sandals/hard soled slip on shoes (because having to jam swollen feet into boots for a 3am loo run is not the most fun)
Meds (both prescription, if needed, and antihistamines, painkillers, anti-nausea, and decongestants
ADDITIONAL EDIT: …and if you’re planning on trying for a politics role and/or taking to combat, Strepsils or a similar throat sweet. There is a chance of yelling yourself hoarse)
Suncream
Anti-nibbly insect spray/gloop/oil of choice
Chemical hand warmers and/or chemical ice packs
More blankets than you think you’ll need
OC cash (signal in field can always be dodgy. Make OC vendors and OC food sellers lives easier, have cash to hand of their digital boxes go down)
Small notebook and not-sad-if-lost pen/pencil for IC stuff
If you’re like me and sleep with a comfort toy/blanket of some variety, it’s alway worth bringing to have in tent as an anchor of normality
Earplugs you can sleep in and an eye cover you can sleep in
Non-flame light of some sort for tent
Power banks (because whilst you’re usually better leave phone locked/hidden in tent, pre-time in selfies, check ins with folks, “where the fuck are you?!” Pre-time in texts, checking bank balance, etc can drain battery on phone fair quick…also, a lot of lamps/torches are rechargeable now so it’s useful to have a back up in case you forget to turn the tent light off before heading out into Anvil for an evening)