I'm one of those guys that wears a medium sized backpack (with hydration system). Tools are in a fender bag, not on my back. Backpack is for rainjacket, lunch, snack, maps, small first aid kit, etc. Key for me is a backpack that has a nice waist strap (1.5 - 2" wide). This puts the weight on my hips, not on my shoulders.
It is often said that standing lowers your center of gravity. Incorrect. When standing you have made one object (you and the bike glued together by your butt on the seat) into two somewhat independent objects. The bike has a lower CG than you sitting on bike. Your legs let your body act somewhat independently when the bike gets bounced. Like watching a mogul skier ... the skis and legs are bouncing all around and yet the torso and head are barely moving. Picking up the bike without the weight of the gear is much easier. That rack and weight is going to make your bike weigh more and be harder to correct when it gets bounced.
Have you considered the mojave from Giant Loop?
https://www.giantloopmoto.com/product-c ... g-systems/
4 - 1qt Mobil 1 oil bottles (or similar) would get you the 1 g of gasoline and pack pretty easily.
Note I do not have a mojave, but have seen them and they look well made. Plus is no rack to mess with, easy on/off, and no rack weight added to your bike.