FWIW, I recommend the following.

• Assemble your gear for the trip, and don't skimp on repair gear (spare tire, spare tubes, etc)
• Put it in a backpack
• Wear the backpack for a 50-mile ride
• Imagine doing that 6 days in a row

If it works for you, or doesn't feel comfortable, then you have your answer.

IMO though you really aren't benefitting much by paring things down to the point where you only have one pair of underwear, no deodorant and a sore back.

It's also very easy and convenient to use something like the Topeak Trunk Bags, many of which have 12l / 750 cu in of available space, or just find some very small and light panniers. It really is not a big deal to use them, and much more comfortable than a backpack.