Well, just done a live exercise. Went to Asda's (UK equivelent of Walmart?) this afternoon, and bought £400/$600 of food. It filled the rear of the Jeep. After unpacking, it filled the fridge, and just two lockers. Total volume about 12 cubic feet. Didn't weigh it but the car didn't feel heavy. This would last 5 of us about two months. However, there were a number of items we didn't buy such as fresh items which we will still get on an almost daily basis, such as milk, bread, etc.
Since we got home, the kids have done a menu for a year, based on adding in all the other stuff we'd need/want, and it budgets out at around $4,500.
And hey, guess what, we'd get about 10 times what we got today onto the boat. 43ft x 13ft8in. Some of what we got was dried food, but there was not a massive choice in a local supermarket. There is loads of canned stuff though, which is heavyish. I reckon that a full years supplies would be something in the order of just over 2 tonnes, which should not be a problem. Gives me an all up weight of about 23 tonne! (That can't be right - we're supposed to be 33,000lbs light ship?). I'll come back on that one!
My conclusion, is that we can indeed provision for a full year on a 43ft boat, without too much trouble.
However, if provisioning for a year, there would be quite a few other items needed. Medical stuff, spares for engine, genset, plumbing, electrics, rigging, damage control gear, and so on.
Might need to spend a bit more on anti-foul, as I think it will all notice at the waterline. Next job, a full loading list.