Here's a nice example from a very experienced cruiser with 2 1/2 circumnavigations under his belt. It's a list of what they provision for two, for a 12-week cruise. So, for you that'd work out to about 24 weeks. Half again should cover it. They cruise on a nicely modified 29ft Pearson Triton. Click on the "Boat Projects" link to see the integral water tanks that were added.
Atom Voyages | Recipes and Provisioning for Cruising Sailboats