And he's travelling from London and going to the Lakes...
Can you just ring him up and tell him if he can't carry his backpack from his seat to the luggage racks and thinks the aisle or someone else's seat are good places to put it... He's unlikely to be able to carry it round Derwent Water.
While you're at it, explain seat reservations and wireless charging.
(I'm sure they are nice lads, but just a bit clueless).