Case in point: I went to B&Q the other day to get a replacement shower head and a wire brush (for a sheepskin rug). I left with those two items, plus the makings of a Roomba fence, a couple of sink strainers and a box full of assorted screws. Didn't find a multipack of nails or I would have bought those as well (to give me options - do I screw the Roomba fence together or nail it together?).
I somehow managed to avoid buying a laser leveller this time but only because they were missing the particular model I want.
The Roomba fence is to do with a couple of Ikea Poang chairs I've got - the base is made up of flat strips of wood and the Roomba beaches itself on them. The plan is to put a strip of wood on top of those that's high enough to trigger the Roomba's bumper, so it will avoid them instead of trying to barrel straight over.