The backpacks were like 20 kg, so I guess they were taken off. The KGL spend some time there, so they had at least food and water with them. Of course I cant be 100% sure but I think they had the most important stuff with them, probably even a tent and their blanket for the night, as they didnt knew when the frenchies will arrive and if they go straight to a battle with british army.
Still, wrong place to Post this. Historical discussion should be your place.