Unfortunately those days seem to be behind us and most threads turn into some tin hat rant.
So back on topic, I have on my list:
-Sandals/flip flops for non operational wear
- jungle sleeping bag (I quite like the look of the snug pan traveller - non military blue)
- folding sink type affair for washing
- spare socks
- ear plugs, eye mask for sleeping
- lightweight clothing (non poly)
- Kip may or inflating mattress
- I’ve got some soap stuff that can be used on body, clothes, soul
Swimming shorts: For slepping, showering when the showers is more primitive and you could offend someone, training kit, warm weather or even swimming.
Sunhat: if you don't get one, bonnie hat typ but in a non military color.
Spares of PPE, it doesn't mather if you should get them, if you need them you need them know, not when next transport arrives etc.
First aid kit: Same as ppe.
Then I would have some bags with stuff that is more aimed for different jobs. You don't need food for a week if you work at a consert but a singel ready to eat meal can be handy. In other cases it could be a good ide to bring enough for a week but ready to eat is heavy so a mix of freeze dried and ready to eat could work.
Same with cold weather kit and water purification.
Make two/tre bags, label them and just grab the right ones and stuff them down in your large rucksack.