Thinking far enough?
1) The clue's in your question: "the fuels that aircraft and ships need". We already use different fuels for ships and boats (e.g. kerosene, diesel, nuclear, horse-drawn on the canals, and yes, wind) and individuals can change their use as and when they need. You've also forgotten that most food is transported over/in-land by rail/road - so add electricity (or electrified rails), petrol, coal/wood (for steam), and, again, wind. Most countries can also choose between land or sea for added diversity.
Foods necessarily transported by air are luxuries, so not relevant in a famine, and rotting is optional - there's these things called refrigeration and canning...
2) No country 'sends us food'. People send us food, or we go there and take it, in return for money. If every, say, Ethiopian stopped selling us grain, we could get it from, say, Kansas (or vice versa) and no user would notice. Fungible products, and trade, FTW! :-)