Wingnut Hyper 2.5 backpack sits very low, on the lower back only. Soooo much nicer in this hot weather.
Alternatively I use a couple of water bottles on the frame and seat pack (ortleib 1 litre for small rides or the big 3 litre ortlieb one for bigger rides with gilet, etc) for tools etc, and rear jersey pockets for trail food etc.
Arm & leg warmers, buff & gilet are all good if you don’t have much space. All fit in the larger saddle bag with tools too.