For food related stocks, I would go with Monsanto. They had a huge run and seem to be digesting (no pun intended) their gains. They make seeds that increase the yields on crops. With food prices increasing, farmers want to grow more crops per acreage. They have recently predicted a doubling of earning is 5 years. Dupont also has a large agro/biotech division. The fertilizer stocks also have had a huge run, but they recently raised the price of fertilizer by huge amounts and the farmers have no choice but to buy it. Potash is one name in this sector.
For oil, forget about Exxon or any of the large so-called integrated companies. These companies are too big. they also have large chemical and refinery operations which aren't making money because the input for those ops is oil for which the price has skyrocketed. They can't raise the prices on those products to match the huge increase in oil. They are safe plays and won't go out of business, but there are so many other ways to play energy, both for income and growth.
For energy investments, there are several ways to go. The Canadian royalty trust own huge fields of oil and nat gas in Canada and pay out a large % (usually about 70%)l of their earnings in dividends. The dividend yields are over 12% (paid out monthly). This beats Exxon's lousy 2% Dubai recently bought one of these royalty trusts. Some of these are Pengrowth energy, PennWest, Encana, Harvest, Provident, Baytex. Some are listed on both the NYSE and Toronto exchange. Since they pay out a good percentage of their earnings in distributions, they have to continually raise equity and debt to buy new fields to drill on. However, if they do it right and don't overpay, the energy in the fields that they buy should increase in value. Canada increased taxes on these companies to start in 2011, which knocked their share prices down a few years ago, but they have deductions so they won't have to pay the increased taxes right away. Canada will withhold15% of your monthly distribution, but you get a tax credit for it on your US tax return.
There are also several US royalty trusts. These were formed by oil and gas companies that wanted to sell off some properties. Unlike the Canadian royalty trusts, the US trusts don't reinvest and buy new properties. They essentially are milking the fields that they own. Some of these are Hugoton, BP Prudhoe Bay, Dominion Black Warrior, Permian Basis, San Juan, Sabine and Cross Timbers.. Most of these pay monthly dividends that rise or fall with the price of oil and gas and the production for the month. Yields on some of these are increasing to 10-12%(along with the share price) as the price of oil and nat gas increases. The downside to these are that the fields will not last forever. Some only have 7 or 8 years left of production, but some have over 10. The estimates, which are performed each year, sometimes change, and fields have lasted longer. Another downside to these is the tax reporting. You report your distribution as a royalty payment (not a dividend) and it is taxed at regular income tax rates. However, since the fields are depleting, you get a depletion deduction which reduces part of your income. Turbo Tax easily handles the tax work. The US royalty trusts usually have limited expenses (since they don't have employees) so increases in the price of oil and nat gas go right to the distribution you receive. The distributions are paid with a time lag, so the recent increase in nat gas from $7 to over $11 and in oil from $100 to $135 hasn't shown up in the distributions yet, but it will soon (do the math)
There are other energy plays structured as master limited partnerships or MLPs. These also trade on the NYSE and have above average yields that are tax advantaged. Some of these are Atlas, EVEP, Line and Breit Burns. Many of these came public a few years ago and raised equity to purchase properties. Their stocks got hammered (due to hedge fund selling) to the point where they are yielding close to 10% (paid quarterly). Many have recently increased their distributions as their properties start to produce. The ones with investments in the Marcellus shale region in Western Pa and Ohio are good bets as that region is expected to have huge nat gas reserves.
Other nat gas plays include Range Resources (huge Marcellus Shale properties), Chesapeake (CEO bought millions of stock) and Continental. There are some companies drilling in a section of North Dakota called Baken shale area with a huge potential.
Other opportunities include the pipeline MLP companies. There are several of these and they pay good distributions of between 5-9% (tax advantaged because they are partnerships). They get paid to transport the oil and gas regardless of the price of it, so they are less volatile. Many have good histories raising their distributions each year.
Finally, don't forget Petrobras in Brazil. They made a really huge discovery a few months ago. It will take some time to develop, but the stock is already going up. And Santos in Australia has huge nat gas properties and is close to China and its huge energy needs. Santos is rumored to be a takeover target once Australia lifts its ownership restrictions in November.