Unless you're using low-riders, you have the rack top, too, for some bulky things. And you can carry most of your water on the frame.

I came back to bike touring after a career in long distance hiking, and found I could easily tour with only two rear panniers and my sleeping pad on top of the rack. I didn't need a handlebar bag, either. It was nice not having the mass of the front packs and rack.

I did not need to carry as much food on the bike tours I went on, seldom more than two days worth.

One way I reduced my pack size, both hiking and biking, was going stoveless. I used to use an entire front pannier for kitchen stuff.

I also switched to a single-wall shelter. Bikepackers strap such a shelter to the bike frame or handlebars.

Most cyclists carry a lot of clothing. One method I learned is that you should be able to wear all your clothing at once, as part of a coordinated system.

Sorry no input for front-only, just ways to reduce volume.