I've been weeding out some of the monster brambles and nettle patches, which seems pointless when we're about to excavate, but my logic is that the spoil is going into raised beds and I don't want brambles and nettles to be my first crop!
Turns out there is a lot more than weeds down there. The bottom of gardens do tend to become dumping grounds, don't they? Especially when the garden is large. Ours is particularly eclectic in the dumped stuff department. So far I've found a pile of pea shingle, two scaffold boards, roof tiles and, most exciting of all, these.
Not sure about the rest of the haul though.