I did indeed, either in the padded bit inside the main bag or in the pocket where the waterproof cover lives.
Just finished loading it to see how much of my normal kit it'll take and the answer is - all of it, as long as I don't mind something (a lens) going into one of the end pockets rather than the comfy padded inside! Tempted to take it on holiday next year, with the Fuji stuck in there for access during the flight and the rest of it stuffed with spare Solomons etc - I always try to take a complete change of clothes and a couple of extra undies changes just in case the hold baggage goes astray.