My son has ASD and DCD. He’s in year 9 now and we’ve done 3 school trips abroad.
I really second tbe zip lock bags suggestion. We’ve done this with DS each time. We did one for each day with all his clothes including pants, socks , snack bar and money for the day in an envelope marked up so he’s had a small amount of euros incase he loses his card. Marked the bag with day 1, day 2 etc and made sure that DS put the stuff in the bags himself so he knew where everything was. That way there’s only a small amount of stuff loose each day.
Told him to put dirty stuff each day back into the zip lock which mainly he did!
We also made sure he had the bare minimum with him to avoid overwhelm with a small room and lots of kids stuff and that his bag had a red tag on so he could find it easily in the sea of black sports bags!
When he turned 13 we put Apple Pay on his phone.
Each time he’s taken all his coach journey stuff in a small rucksack with cards, snacks etc and a small pencil case with his charger etc in. But he’s taken a small cross body bag each time as well with just wallet and phone in so on the journeys could leave the rucksack in the bus and just take phone and wallet with him to service stations etc plus then for days out he had the option.
We also put his reusable water bottle in his bag for refilling each day but gave him a 1 litre plastic disposable water for the journey out so he didn’t lose his water bottle before he even got there.
He's done great every time and it’s done wonders for his confidence.
I hope your DS has a fab time!
These are the bags we used
40 Pcs Ziplock Bags, 20 * 16 Inch... https://www.amazon.co.uk/dp/B0CMTT3JC8?ref=ppx_pop_mob_ap_share