If you are ruling out ANY sort of rack or backpack, there aren't many options left!
I second the idea of the seatpost-mounted "beam" rack and a rack trunk, or a large saddlebag like the Carradice or other type of seat-post bag.
The only other option is a large handelbar bag, but your bike will probably handle much better with the load in back than hanging off the bars.
Detours makes a huge seat-post bag: http://detours.us/store/seat-post-bags/high-tail-exp/