I need to go through my handlebar bag, but I think I'm down to really just keeping a cable lock, spare tube, security wrench for the bolt on skewers, and a tire lever in there. I suspect there are some superfluous things in there I have collected and just put in, but I can't think of what it might be right now. Apart from clothes and lunch, I see no need to carry any more than I would on a road ride, which is a way to fix a flat and a multi tool (though, apart from adjusting the saddle height, I can't think to a time I ever needed to use a multi tool during a ride). My commute isn't a tour nor is it a century. 12 miles, each way.